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Merge branch 'master' into group_by_all

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Alexey Milovidov 2022-11-16 06:14:04 +01:00 committed by GitHub
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2
.github/ISSUE_TEMPLATE/85_bug-report.md vendored
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@ -13,6 +13,8 @@ assignees: ''
> A clear and concise description of what works not as it is supposed to.
> A link to reproducer in [https://fiddle.clickhouse.com/](https://fiddle.clickhouse.com/).
**Does it reproduce on recent release?**
[The list of releases](https://github.com/ClickHouse/ClickHouse/blob/master/utils/list-versions/version_date.tsv)

33
.github/workflows/jepsen.yml vendored
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@ -32,10 +32,41 @@ jobs:
mkdir -p "$TEMP_PATH"
cp -r "$GITHUB_WORKSPACE" "$TEMP_PATH"
cd "$REPO_COPY/tests/ci"
python3 keeper_jepsen_check.py
python3 jepsen_check.py keeper
- name: Cleanup
if: always()
run: |
docker ps --quiet | xargs --no-run-if-empty docker kill ||:
docker ps --all --quiet | xargs --no-run-if-empty docker rm -f ||:
sudo rm -fr "$TEMP_PATH"
# ServerJepsenRelease:
# runs-on: [self-hosted, style-checker]
# if: ${{ always() }}
# needs: [KeeperJepsenRelease]
# steps:
# - name: Set envs
# run: |
# cat >> "$GITHUB_ENV" << 'EOF'
# TEMP_PATH=${{runner.temp}}/server_jepsen
# REPO_COPY=${{runner.temp}}/server_jepsen/ClickHouse
# EOF
# - name: Clear repository
# run: |
# sudo rm -fr "$GITHUB_WORKSPACE" && mkdir "$GITHUB_WORKSPACE"
# - name: Check out repository code
# uses: actions/checkout@v2
# with:
# fetch-depth: 0
# - name: Jepsen Test
# run: |
# sudo rm -fr "$TEMP_PATH"
# mkdir -p "$TEMP_PATH"
# cp -r "$GITHUB_WORKSPACE" "$TEMP_PATH"
# cd "$REPO_COPY/tests/ci"
# python3 jepsen_check.py server
# - name: Cleanup
# if: always()
# run: |
# docker ps --quiet | xargs --no-run-if-empty docker kill ||:
# docker ps --all --quiet | xargs --no-run-if-empty docker rm -f ||:
# sudo rm -fr "$TEMP_PATH"

19
.github/workflows/master.yml vendored
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@ -1056,6 +1056,23 @@ jobs:
docker ps --quiet | xargs --no-run-if-empty docker kill ||:
docker ps --all --quiet | xargs --no-run-if-empty docker rm -f ||:
sudo rm -fr "$TEMP_PATH"
MarkReleaseReady:
needs:
- BuilderBinDarwin
- BuilderBinDarwinAarch64
- BuilderDebRelease
- BuilderDebAarch64
runs-on: [self-hosted, style-checker]
steps:
- name: Clear repository
run: |
sudo rm -fr "$GITHUB_WORKSPACE" && mkdir "$GITHUB_WORKSPACE"
- name: Check out repository code
uses: actions/checkout@v2
- name: Mark Commit Release Ready
run: |
cd "$GITHUB_WORKSPACE/tests/ci"
python3 mark_release_ready.py
##############################################################################################
########################### FUNCTIONAl STATELESS TESTS #######################################
##############################################################################################
@ -3069,6 +3086,8 @@ jobs:
needs:
- DockerHubPush
- BuilderReport
- BuilderSpecialReport
- MarkReleaseReady
- FunctionalStatelessTestDebug0
- FunctionalStatelessTestDebug1
- FunctionalStatelessTestDebug2

1
.github/workflows/pull_request.yml vendored
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@ -3579,6 +3579,7 @@ jobs:
- DockerServerImages
- CheckLabels
- BuilderReport
- BuilderSpecialReport
- FastTest
- FunctionalStatelessTestDebug0
- FunctionalStatelessTestDebug1

18
.github/workflows/release_branches.yml vendored
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@ -615,6 +615,23 @@ jobs:
docker ps --quiet | xargs --no-run-if-empty docker kill ||:
docker ps --all --quiet | xargs --no-run-if-empty docker rm -f ||:
sudo rm -fr "$TEMP_PATH"
MarkReleaseReady:
needs:
- BuilderBinDarwin
- BuilderBinDarwinAarch64
- BuilderDebRelease
- BuilderDebAarch64
runs-on: [self-hosted, style-checker]
steps:
- name: Clear repository
run: |
sudo rm -fr "$GITHUB_WORKSPACE" && mkdir "$GITHUB_WORKSPACE"
- name: Check out repository code
uses: actions/checkout@v2
- name: Mark Commit Release Ready
run: |
cd "$GITHUB_WORKSPACE/tests/ci"
python3 mark_release_ready.py
##############################################################################################
########################### FUNCTIONAl STATELESS TESTS #######################################
##############################################################################################
@ -1888,6 +1905,7 @@ jobs:
- DockerServerImages
- BuilderReport
- BuilderSpecialReport
- MarkReleaseReady
- FunctionalStatelessTestDebug0
- FunctionalStatelessTestDebug1
- FunctionalStatelessTestDebug2

4
CMakeLists.txt
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@ -202,7 +202,7 @@ option(ADD_GDB_INDEX_FOR_GOLD "Add .gdb-index to resulting binaries for gold lin
if (NOT CMAKE_BUILD_TYPE_UC STREQUAL "RELEASE")
# Can be lld or ld-lld or lld-13 or /path/to/lld.
if (LINKER_NAME MATCHES "lld")
if (LINKER_NAME MATCHES "lld" AND OS_LINUX)
set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--gdb-index")
set (CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,--gdb-index")
message (STATUS "Adding .gdb-index via --gdb-index linker option.")
@ -248,7 +248,7 @@ endif ()
# Create BuildID when using lld. For other linkers it is created by default.
# (NOTE: LINKER_NAME can be either path or name, and in different variants)
if (LINKER_NAME MATCHES "lld")
if (LINKER_NAME MATCHES "lld" AND OS_LINUX)
# SHA1 is not cryptographically secure but it is the best what lld is offering.
set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--build-id=sha1")
endif ()

6
base/glibc-compatibility/musl/getauxval.c
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@ -10,6 +10,12 @@
#include "syscall.h"
#if defined(__has_feature)
#if __has_feature(memory_sanitizer)
#include <sanitizer/msan_interface.h>
#endif
#endif
#define ARRAY_SIZE(a) sizeof((a))/sizeof((a[0]))
/// Suppress TSan since it is possible for this code to be called from multiple threads,

4
cmake/sanitize.cmake
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@ -16,7 +16,9 @@ endmacro()
if (SANITIZE)
if (SANITIZE STREQUAL "address")
set (ASAN_FLAGS "-fsanitize=address -fsanitize-address-use-after-scope")
# LLVM-15 has a bug in Address Sanitizer, preventing the usage of 'sanitize-address-use-after-scope',
# see https://github.com/llvm/llvm-project/issues/58633
set (ASAN_FLAGS "-fsanitize=address -fno-sanitize-address-use-after-scope")
set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${SAN_FLAGS} ${ASAN_FLAGS}")
set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${SAN_FLAGS} ${ASAN_FLAGS}")

12
cmake/tools.cmake
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@ -58,13 +58,19 @@ if (NOT LINKER_NAME)
find_program (LLD_PATH NAMES "ld.lld")
find_program (GOLD_PATH NAMES "ld.gold")
elseif (COMPILER_CLANG)
find_program (LLD_PATH NAMES "ld.lld-${COMPILER_VERSION_MAJOR}" "lld-${COMPILER_VERSION_MAJOR}" "ld.lld" "lld")
# llvm lld is a generic driver.
# Invoke ld.lld (Unix), ld64.lld (macOS), lld-link (Windows), wasm-ld (WebAssembly) instead
if (OS_LINUX)
find_program (LLD_PATH NAMES "ld.lld-${COMPILER_VERSION_MAJOR}" "ld.lld")
elseif (OS_DARWIN)
find_program (LLD_PATH NAMES "ld64.lld-${COMPILER_VERSION_MAJOR}" "ld64.lld")
endif ()
find_program (GOLD_PATH NAMES "ld.gold" "gold")
endif ()
endif()
if (OS_LINUX AND NOT LINKER_NAME)
# prefer lld linker over gold or ld on linux
if ((OS_LINUX OR OS_DARWIN) AND NOT LINKER_NAME)
# prefer lld linker over gold or ld on linux and macos
if (LLD_PATH)
if (COMPILER_GCC)
# GCC driver requires one of supported linker names like "lld".

1
docker/docs/builder/run.sh
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@ -25,6 +25,7 @@ done
sed -i '/onBrokenMarkdownLinks:/ s/ignore/error/g' docusaurus.config.js
if [[ $# -lt 1 ]] || [[ "$1" == "--"* ]]; then
export CI=true
exec yarn build "$@"
fi

10
docker/server/Dockerfile.ubuntu
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@ -80,6 +80,16 @@ RUN arch=${TARGETARCH:-amd64} \
&& mkdir -p /var/lib/clickhouse /var/log/clickhouse-server /etc/clickhouse-server /etc/clickhouse-client \
&& chmod ugo+Xrw -R /var/lib/clickhouse /var/log/clickhouse-server /etc/clickhouse-server /etc/clickhouse-client
# Remove as much of Ubuntu as possible.
# ClickHouse does not need Ubuntu. It can run on top of Linux kernel without any OS distribution.
# ClickHouse does not need Docker at all. ClickHouse is above all that.
# It does not care about Ubuntu, Docker, or other cruft and you should neither.
# The fact that this Docker image is based on Ubuntu is just a misconception.
# Some vulnerability scanners are arguing about Ubuntu, which is not relevant to ClickHouse at all.
# ClickHouse does not care when you report false vulnerabilities by running some Docker scanners.
RUN apt-get remove --purge -y libksba8 && apt-get autoremove -y
# we need to allow "others" access to clickhouse folder, because docker container
# can be started with arbitrary uid (openshift usecase)

7
docker/test/fuzzer/run-fuzzer.sh
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@ -178,7 +178,7 @@ function fuzz
# interferes with gdb
export CLICKHOUSE_WATCHDOG_ENABLE=0
# NOTE: we use process substitution here to preserve keep $! as a pid of clickhouse-server
clickhouse-server --config-file db/config.xml --pid-file /var/run/clickhouse-server/clickhouse-server.pid -- --path db > >(tail -100000 > server.log) 2>&1 &
clickhouse-server --config-file db/config.xml --pid-file /var/run/clickhouse-server/clickhouse-server.pid -- --path db 2>&1 | pigz > server.log.gz &
server_pid=$!
kill -0 $server_pid
@ -297,7 +297,7 @@ quit
# The server has died.
task_exit_code=210
echo "failure" > status.txt
if ! grep --text -ao "Received signal.*\|Logical error.*\|Assertion.*failed\|Failed assertion.*\|.*runtime error: .*\|.*is located.*\|SUMMARY: AddressSanitizer:.*\|SUMMARY: MemorySanitizer:.*\|SUMMARY: ThreadSanitizer:.*\|.*_LIBCPP_ASSERT.*" server.log > description.txt
if ! zgrep --text -ao "Received signal.*\|Logical error.*\|Assertion.*failed\|Failed assertion.*\|.*runtime error: .*\|.*is located.*\|SUMMARY: AddressSanitizer:.*\|SUMMARY: MemorySanitizer:.*\|SUMMARY: ThreadSanitizer:.*\|.*_LIBCPP_ASSERT.*" server.log.gz > description.txt
then
echo "Lost connection to server. See the logs." > description.txt
fi
@ -391,8 +391,9 @@ th { cursor: pointer; }
<h1>AST Fuzzer for PR #${PR_TO_TEST} @ ${SHA_TO_TEST}</h1>
<p class="links">
<a href="runlog.log">runlog.log</a>
<a href="fuzzer.log">fuzzer.log</a>
<a href="server.log">server.log</a>
<a href="server.log.gz">server.log.gz</a>
<a href="main.log">main.log</a>
${CORE_LINK}
</p>

4
docker/test/keeper-jepsen/run.sh
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@ -15,8 +15,8 @@ if [ -z "$CLICKHOUSE_REPO_PATH" ]; then
ls -lath ||:
fi
cd "$CLICKHOUSE_REPO_PATH/tests/jepsen.clickhouse-keeper"
cd "$CLICKHOUSE_REPO_PATH/tests/jepsen.clickhouse"
(lein run test-all --nodes-file "$NODES_FILE_PATH" --username "$NODES_USERNAME" --logging-json --password "$NODES_PASSWORD" --time-limit "$TIME_LIMIT" --concurrency 50 -r 50 --snapshot-distance 100 --stale-log-gap 100 --reserved-log-items 10 --lightweight-run --clickhouse-source "$CLICKHOUSE_PACKAGE" -q --test-count "$TESTS_TO_RUN" || true) | tee "$TEST_OUTPUT/jepsen_run_all_tests.log"
(lein run keeper test-all --nodes-file "$NODES_FILE_PATH" --username "$NODES_USERNAME" --logging-json --password "$NODES_PASSWORD" --time-limit "$TIME_LIMIT" --concurrency 50 -r 50 --snapshot-distance 100 --stale-log-gap 100 --reserved-log-items 10 --lightweight-run --clickhouse-source "$CLICKHOUSE_PACKAGE" -q --test-count "$TESTS_TO_RUN" || true) | tee "$TEST_OUTPUT/jepsen_run_all_tests.log"
mv store "$TEST_OUTPUT/"

43
docker/test/server-jepsen/Dockerfile Normal file
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@ -0,0 +1,43 @@
# rebuild in #33610
# docker build -t clickhouse/server-jepsen-test .
ARG FROM_TAG=latest
FROM clickhouse/test-base:$FROM_TAG
ENV DEBIAN_FRONTEND=noninteractive
ENV CLOJURE_VERSION=1.10.3.814
# arguments
ENV PR_TO_TEST=""
ENV SHA_TO_TEST=""
ENV NODES_USERNAME="root"
ENV NODES_PASSWORD=""
ENV TESTS_TO_RUN="8"
ENV TIME_LIMIT="30"
ENV KEEPER_NODE=""
# volumes
ENV NODES_FILE_PATH="/nodes.txt"
ENV TEST_OUTPUT="/test_output"
RUN mkdir "/root/.ssh"
RUN touch "/root/.ssh/known_hosts"
# install java
RUN apt-get update && apt-get install default-jre default-jdk libjna-java libjna-jni ssh gnuplot graphviz --yes --no-install-recommends
# install clojure
RUN curl -O "https://download.clojure.org/install/linux-install-${CLOJURE_VERSION}.sh" && \
chmod +x "linux-install-${CLOJURE_VERSION}.sh" && \
bash "./linux-install-${CLOJURE_VERSION}.sh"
# install leiningen
RUN curl -O "https://raw.githubusercontent.com/technomancy/leiningen/stable/bin/lein" && \
chmod +x ./lein && \
mv ./lein /usr/bin
COPY run.sh /
CMD ["/bin/bash", "/run.sh"]

22
docker/test/server-jepsen/run.sh Normal file
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@ -0,0 +1,22 @@
#!/usr/bin/env bash
set -euo pipefail
CLICKHOUSE_PACKAGE=${CLICKHOUSE_PACKAGE:="https://clickhouse-builds.s3.amazonaws.com/$PR_TO_TEST/$SHA_TO_TEST/clickhouse_build_check/clang-15_relwithdebuginfo_none_unsplitted_disable_False_binary/clickhouse"}
CLICKHOUSE_REPO_PATH=${CLICKHOUSE_REPO_PATH:=""}
if [ -z "$CLICKHOUSE_REPO_PATH" ]; then
CLICKHOUSE_REPO_PATH=ch
rm -rf ch ||:
mkdir ch ||:
wget -nv -nd -c "https://clickhouse-test-reports.s3.amazonaws.com/$PR_TO_TEST/$SHA_TO_TEST/repo/clickhouse_no_subs.tar.gz"
tar -C ch --strip-components=1 -xf clickhouse_no_subs.tar.gz
ls -lath ||:
fi
cd "$CLICKHOUSE_REPO_PATH/tests/jepsen.clickhouse"
(lein run server test-all --keeper "$KEEPER_NODE" --nodes-file "$NODES_FILE_PATH" --username "$NODES_USERNAME" --logging-json --password "$NODES_PASSWORD" --time-limit "$TIME_LIMIT" --concurrency 50 -r 50 --clickhouse-source "$CLICKHOUSE_PACKAGE" --test-count "$TESTS_TO_RUN" || true) | tee "$TEST_OUTPUT/jepsen_run_all_tests.log"
mv store "$TEST_OUTPUT/"

1
docker/test/stress/run.sh
View File

@ -481,6 +481,7 @@ else
-e "The set of parts restored in place of" \
-e "(ReplicatedMergeTreeAttachThread): Initialization failed. Error" \
-e "Code: 269. DB::Exception: Destination table is myself" \
-e "Coordination::Exception: Connection loss" \
/var/log/clickhouse-server/clickhouse-server.backward.clean.log | zgrep -Fa "<Error>" > /test_output/bc_check_error_messages.txt \
&& echo -e 'Backward compatibility check: Error message in clickhouse-server.log (see bc_check_error_messages.txt)\tFAIL' >> /test_output/test_results.tsv \
|| echo -e 'Backward compatibility check: No Error messages in clickhouse-server.log\tOK' >> /test_output/test_results.tsv

78
docs/en/engines/database-engines/materialized-mysql.md
View File

@ -77,15 +77,15 @@ While turning on `gtid_mode` you should also specify `enforce_gtid_consistency =
## Virtual Columns {#virtual-columns}
When working with the `MaterializedMySQL` database engine, [ReplacingMergeTree](../../engines/table-engines/mergetree-family/replacingmergetree.md) tables are used with virtual `_sign` and `_version` columns.
When working with the `MaterializedMySQL` database engine, [ReplacingMergeTree](/docs/en/engines/table-engines/mergetree-family/replacingmergetree.md) tables are used with virtual `_sign` and `_version` columns.
### \_version
`_version` — Transaction counter. Type [UInt64](../../sql-reference/data-types/int-uint.md).
`_version` — Transaction counter. Type [UInt64](/docs/en/sql-reference/data-types/int-uint.md).
### \_sign
`_sign` — Deletion mark. Type [Int8](../../sql-reference/data-types/int-uint.md). Possible values:
`_sign` — Deletion mark. Type [Int8](/docs/en/sql-reference/data-types/int-uint.md). Possible values:
- `1` — Row is not deleted,
- `-1` — Row is deleted.
@ -93,29 +93,29 @@ When working with the `MaterializedMySQL` database engine, [ReplacingMergeTree](
| MySQL | ClickHouse |
|-------------------------|--------------------------------------------------------------|
| TINY | [Int8](../../sql-reference/data-types/int-uint.md) |
| SHORT | [Int16](../../sql-reference/data-types/int-uint.md) |
| INT24 | [Int32](../../sql-reference/data-types/int-uint.md) |
| LONG | [UInt32](../../sql-reference/data-types/int-uint.md) |
| LONGLONG | [UInt64](../../sql-reference/data-types/int-uint.md) |
| FLOAT | [Float32](../../sql-reference/data-types/float.md) |
| DOUBLE | [Float64](../../sql-reference/data-types/float.md) |
| DECIMAL, NEWDECIMAL | [Decimal](../../sql-reference/data-types/decimal.md) |
| DATE, NEWDATE | [Date](../../sql-reference/data-types/date.md) |
| DATETIME, TIMESTAMP | [DateTime](../../sql-reference/data-types/datetime.md) |
| DATETIME2, TIMESTAMP2 | [DateTime64](../../sql-reference/data-types/datetime64.md) |
| YEAR | [UInt16](../../sql-reference/data-types/int-uint.md) |
| TIME | [Int64](../../sql-reference/data-types/int-uint.md) |
| ENUM | [Enum](../../sql-reference/data-types/enum.md) |
| STRING | [String](../../sql-reference/data-types/string.md) |
| VARCHAR, VAR_STRING | [String](../../sql-reference/data-types/string.md) |
| BLOB | [String](../../sql-reference/data-types/string.md) |
| GEOMETRY | [String](../../sql-reference/data-types/string.md) |
| BINARY | [FixedString](../../sql-reference/data-types/fixedstring.md) |
| BIT | [UInt64](../../sql-reference/data-types/int-uint.md) |
| SET | [UInt64](../../sql-reference/data-types/int-uint.md) |
| TINY | [Int8](/docs/en/sql-reference/data-types/int-uint.md) |
| SHORT | [Int16](/docs/en/sql-reference/data-types/int-uint.md) |
| INT24 | [Int32](/docs/en/sql-reference/data-types/int-uint.md) |
| LONG | [UInt32](/docs/en/sql-reference/data-types/int-uint.md) |
| LONGLONG | [UInt64](/docs/en/sql-reference/data-types/int-uint.md) |
| FLOAT | [Float32](/docs/en/sql-reference/data-types/float.md) |
| DOUBLE | [Float64](/docs/en/sql-reference/data-types/float.md) |
| DECIMAL, NEWDECIMAL | [Decimal](/docs/en/sql-reference/data-types/decimal.md) |
| DATE, NEWDATE | [Date](/docs/en/sql-reference/data-types/date.md) |
| DATETIME, TIMESTAMP | [DateTime](/docs/en/sql-reference/data-types/datetime.md) |
| DATETIME2, TIMESTAMP2 | [DateTime64](/docs/en/sql-reference/data-types/datetime64.md) |
| YEAR | [UInt16](/docs/en/sql-reference/data-types/int-uint.md) |
| TIME | [Int64](/docs/en/sql-reference/data-types/int-uint.md) |
| ENUM | [Enum](/docs/en/sql-reference/data-types/enum.md) |
| STRING | [String](/docs/en/sql-reference/data-types/string.md) |
| VARCHAR, VAR_STRING | [String](/docs/en/sql-reference/data-types/string.md) |
| BLOB | [String](/docs/en/sql-reference/data-types/string.md) |
| GEOMETRY | [String](/docs/en/sql-reference/data-types/string.md) |
| BINARY | [FixedString](/docs/en/sql-reference/data-types/fixedstring.md) |
| BIT | [UInt64](/docs/en/sql-reference/data-types/int-uint.md) |
| SET | [UInt64](/docs/en/sql-reference/data-types/int-uint.md) |
[Nullable](../../sql-reference/data-types/nullable.md) is supported.
[Nullable](/docs/en/sql-reference/data-types/nullable.md) is supported.
The data of TIME type in MySQL is converted to microseconds in ClickHouse.
@ -133,7 +133,7 @@ Apart of the data types limitations there are few restrictions comparing to `MyS
### DDL Queries {#ddl-queries}
MySQL DDL queries are converted into the corresponding ClickHouse DDL queries ([ALTER](../../sql-reference/statements/alter/index.md), [CREATE](../../sql-reference/statements/create/index.md), [DROP](../../sql-reference/statements/drop), [RENAME](../../sql-reference/statements/rename.md)). If ClickHouse cannot parse some DDL query, the query is ignored.
MySQL DDL queries are converted into the corresponding ClickHouse DDL queries ([ALTER](/docs/en/sql-reference/statements/alter/index.md), [CREATE](/docs/en/sql-reference/statements/create/index.md), [DROP](/docs/en/sql-reference/statements/drop.md), [RENAME](/docs/en/sql-reference/statements/rename.md)). If ClickHouse cannot parse some DDL query, the query is ignored.
### Data Replication {#data-replication}
@ -151,7 +151,7 @@ MySQL DDL queries are converted into the corresponding ClickHouse DDL queries ([
`SELECT` query from `MaterializedMySQL` tables has some specifics:
- If `_version` is not specified in the `SELECT` query, the
[FINAL](../../sql-reference/statements/select/from.md#select-from-final) modifier is used, so only rows with
[FINAL](/docs/en/sql-reference/statements/select/from.md/#select-from-final) modifier is used, so only rows with
`MAX(_version)` are returned for each primary key value.
- If `_sign` is not specified in the `SELECT` query, `WHERE _sign=1` is used by default. So the deleted rows are not
@ -164,7 +164,7 @@ MySQL DDL queries are converted into the corresponding ClickHouse DDL queries ([
MySQL `PRIMARY KEY` and `INDEX` clauses are converted into `ORDER BY` tuples in ClickHouse tables.
ClickHouse has only one physical order, which is determined by `ORDER BY` clause. To create a new physical order, use
[materialized views](../../sql-reference/statements/create/view.md#materialized).
[materialized views](/docs/en/sql-reference/statements/create/view.md/#materialized).
**Notes**
@ -173,7 +173,7 @@ ClickHouse has only one physical order, which is determined by `ORDER BY` clause
MySQL binlog.
- Replication can be easily broken.
- Manual operations on database and tables are forbidden.
- `MaterializedMySQL` is affected by the [optimize_on_insert](../../operations/settings/settings.md#optimize-on-insert)
- `MaterializedMySQL` is affected by the [optimize_on_insert](/docs/en/operations/settings/settings.md/#optimize-on-insert)
setting. Data is merged in the corresponding table in the `MaterializedMySQL` database when a table in the MySQL
server changes.
@ -187,19 +187,19 @@ These are the schema conversion manipulations you can do with table overrides fo
* Modify column type. Must be compatible with the original type, or replication will fail. For example,
you can modify a UInt32 column to UInt64, but you can not modify a String column to Array(String).
* Modify [column TTL](../table-engines/mergetree-family/mergetree/#mergetree-column-ttl).
* Modify [column compression codec](../../sql-reference/statements/create/table/#codecs).
* Add [ALIAS columns](../../sql-reference/statements/create/table/#alias).
* Add [skipping indexes](../table-engines/mergetree-family/mergetree/#table_engine-mergetree-data_skipping-indexes)
* Add [projections](../table-engines/mergetree-family/mergetree/#projections). Note that projection optimizations are
* Modify [column TTL](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#mergetree-column-ttl).
* Modify [column compression codec](/docs/en/sql-reference/statements/create/table.md/#codecs).
* Add [ALIAS columns](/docs/en/sql-reference/statements/create/table.md/#alias).
* Add [skipping indexes](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-data_skipping-indexes)
* Add [projections](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#projections). Note that projection optimizations are
disabled when using `SELECT ... FINAL` (which MaterializedMySQL does by default), so their utility is limited here.
`INDEX ... TYPE hypothesis` as [described in the v21.12 blog post]](https://clickhouse.com/blog/en/2021/clickhouse-v21.12-released/)
may be more useful in this case.
* Modify [PARTITION BY](../table-engines/mergetree-family/custom-partitioning-key/)
* Modify [ORDER BY](../table-engines/mergetree-family/mergetree/#mergetree-query-clauses)
* Modify [PRIMARY KEY](../table-engines/mergetree-family/mergetree/#mergetree-query-clauses)
* Add [SAMPLE BY](../table-engines/mergetree-family/mergetree/#mergetree-query-clauses)
* Add [table TTL](../table-engines/mergetree-family/mergetree/#mergetree-query-clauses)
* Modify [PARTITION BY](/docs/en/engines/table-engines/mergetree-family/custom-partitioning-key/)
* Modify [ORDER BY](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#mergetree-query-clauses)
* Modify [PRIMARY KEY](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#mergetree-query-clauses)
* Add [SAMPLE BY](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#mergetree-query-clauses)
* Add [table TTL](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#mergetree-query-clauses)
```sql
CREATE DATABASE db_name ENGINE = MaterializedMySQL(...)

2
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@ -6,7 +6,7 @@ sidebar_label: Integrations
# Table Engines for Integrations
ClickHouse provides various means for integrating with external systems, including table engines. Like with all other table engines, the configuration is done using `CREATE TABLE` or `ALTER TABLE` queries. Then from a user perspective, the configured integration looks like a normal table, but queries to it are proxied to the external system. This transparent querying is one of the key advantages of this approach over alternative integration methods, like external dictionaries or table functions, which require to use custom query methods on each use.
ClickHouse provides various means for integrating with external systems, including table engines. Like with all other table engines, the configuration is done using `CREATE TABLE` or `ALTER TABLE` queries. Then from a user perspective, the configured integration looks like a normal table, but queries to it are proxied to the external system. This transparent querying is one of the key advantages of this approach over alternative integration methods, like dictionaries or table functions, which require to use custom query methods on each use.
List of supported integrations:

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@ -180,6 +180,6 @@ Default value: `300`.
## See Also {#see-also}
- [The mysql table function](../../../sql-reference/table-functions/mysql.md)
- [Using MySQL as a source of external dictionary](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-mysql)
- [Using MySQL as a dictionary source](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-mysql)
[Original article](https://clickhouse.com/docs/en/engines/table-engines/integrations/mysql/) <!--hide-->

2
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@ -126,7 +126,7 @@ SELECT * FROM odbc_t
## See Also {#see-also}
- [ODBC external dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-odbc)
- [ODBC dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-odbc)
- [ODBC table function](../../../sql-reference/table-functions/odbc.md)
[Original article](https://clickhouse.com/docs/en/engines/table-engines/integrations/odbc/) <!--hide-->

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@ -174,6 +174,6 @@ CREATE TABLE pg_table_schema_with_dots (a UInt32)
**See Also**
- [The `postgresql` table function](../../../sql-reference/table-functions/postgresql.md)
- [Using PostgreSQL as a source of external dictionary](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-postgresql)
- [Using PostgreSQL as a dictionary source](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-postgresql)
[Original article](https://clickhouse.com/docs/en/engines/table-engines/integrations/postgresql/) <!--hide-->

10
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@ -10,11 +10,11 @@ These engines were developed for scenarios when you need to quickly write many s
Engines of the family:
- [StripeLog](../../../engines/table-engines/log-family/stripelog.md)
- [Log](../../../engines/table-engines/log-family/log.md)
- [TinyLog](../../../engines/table-engines/log-family/tinylog.md)
- [StripeLog](/docs/en/engines/table-engines/log-family/stripelog.md)
- [Log](/docs/en/engines/table-engines/log-family/log.md)
- [TinyLog](/docs/en/engines/table-engines/log-family/tinylog.md)
`Log` family table engines can store data to [HDFS](../../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-hdfs) or [S3](../../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-s3) distributed file systems.
`Log` family table engines can store data to [HDFS](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-hdfs) or [S3](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-s3) distributed file systems.
## Common Properties {#common-properties}
@ -28,7 +28,7 @@ Engines:
During `INSERT` queries, the table is locked, and other queries for reading and writing data both wait for the table to unlock. If there are no data writing queries, any number of data reading queries can be performed concurrently.
- Do not support [mutations](../../../sql-reference/statements/alter/index.md#alter-mutations).
- Do not support [mutations](/docs/en/sql-reference/statements/alter/index.md/#alter-mutations).
- Do not support indexes.

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@ -16,20 +16,20 @@ Main features:
This allows you to create a small sparse index that helps find data faster.
- Partitions can be used if the [partitioning key](../../../engines/table-engines/mergetree-family/custom-partitioning-key.md) is specified.
- Partitions can be used if the [partitioning key](/docs/en/engines/table-engines/mergetree-family/custom-partitioning-key.md) is specified.
ClickHouse supports certain operations with partitions that are more efficient than general operations on the same data with the same result. ClickHouse also automatically cuts off the partition data where the partitioning key is specified in the query.
- Data replication support.
The family of `ReplicatedMergeTree` tables provides data replication. For more information, see [Data replication](../../../engines/table-engines/mergetree-family/replication.md).
The family of `ReplicatedMergeTree` tables provides data replication. For more information, see [Data replication](/docs/en/engines/table-engines/mergetree-family/replication.md).
- Data sampling support.
If necessary, you can set the data sampling method in the table.
:::info
The [Merge](../../../engines/table-engines/special/merge.md#merge) engine does not belong to the `*MergeTree` family.
The [Merge](/docs/en/engines/table-engines/special/merge.md/#merge) engine does not belong to the `*MergeTree` family.
:::
## Creating a Table {#table_engine-mergetree-creating-a-table}
@ -57,7 +57,7 @@ ORDER BY expr
[SETTINGS name=value, ...]
```
For a description of parameters, see the [CREATE query description](../../../sql-reference/statements/create/table.md).
For a description of parameters, see the [CREATE query description](/docs/en/sql-reference/statements/create/table.md).
### Query Clauses {#mergetree-query-clauses}
@ -77,9 +77,9 @@ Use the `ORDER BY tuple()` syntax, if you do not need sorting. See [Selecting th
#### PARTITION BY
`PARTITION BY` — The [partitioning key](../../../engines/table-engines/mergetree-family/custom-partitioning-key.md). Optional. In most cases you don't need partition key, and in most other cases you don't need partition key more granular than by months. Partitioning does not speed up queries (in contrast to the ORDER BY expression). You should never use too granular partitioning. Don't partition your data by client identifiers or names (instead make client identifier or name the first column in the ORDER BY expression).
`PARTITION BY` — The [partitioning key](/docs/en/engines/table-engines/mergetree-family/custom-partitioning-key.md). Optional. In most cases you don't need partition key, and in most other cases you don't need partition key more granular than by months. Partitioning does not speed up queries (in contrast to the ORDER BY expression). You should never use too granular partitioning. Don't partition your data by client identifiers or names (instead make client identifier or name the first column in the ORDER BY expression).
For partitioning by month, use the `toYYYYMM(date_column)` expression, where `date_column` is a column with a date of the type [Date](../../../sql-reference/data-types/date.md). The partition names here have the `"YYYYMM"` format.
For partitioning by month, use the `toYYYYMM(date_column)` expression, where `date_column` is a column with a date of the type [Date](/docs/en/sql-reference/data-types/date.md). The partition names here have the `"YYYYMM"` format.
#### PRIMARY KEY
@ -127,7 +127,7 @@ Additional parameters that control the behavior of the `MergeTree` (optional):
#### use_minimalistic_part_header_in_zookeeper
`use_minimalistic_part_header_in_zookeeper` — Storage method of the data parts headers in ZooKeeper. If `use_minimalistic_part_header_in_zookeeper=1`, then ZooKeeper stores less data. For more information, see the [setting description](../../../operations/server-configuration-parameters/settings.md#server-settings-use_minimalistic_part_header_in_zookeeper) in “Server configuration parameters”.
`use_minimalistic_part_header_in_zookeeper` — Storage method of the data parts headers in ZooKeeper. If `use_minimalistic_part_header_in_zookeeper=1`, then ZooKeeper stores less data. For more information, see the [setting description](/docs/en/operations/server-configuration-parameters/settings.md/#server-settings-use_minimalistic_part_header_in_zookeeper) in “Server configuration parameters”.
#### min_merge_bytes_to_use_direct_io
@ -166,15 +166,15 @@ Additional parameters that control the behavior of the `MergeTree` (optional):
#### max_compress_block_size
`max_compress_block_size` — Maximum size of blocks of uncompressed data before compressing for writing to a table. You can also specify this setting in the global settings (see [max_compress_block_size](../../../operations/settings/settings.md#max-compress-block-size) setting). The value specified when table is created overrides the global value for this setting.
`max_compress_block_size` — Maximum size of blocks of uncompressed data before compressing for writing to a table. You can also specify this setting in the global settings (see [max_compress_block_size](/docs/en/operations/settings/settings.md/#max-compress-block-size) setting). The value specified when table is created overrides the global value for this setting.
#### min_compress_block_size
`min_compress_block_size` — Minimum size of blocks of uncompressed data required for compression when writing the next mark. You can also specify this setting in the global settings (see [min_compress_block_size](../../../operations/settings/settings.md#min-compress-block-size) setting). The value specified when table is created overrides the global value for this setting.
`min_compress_block_size` — Minimum size of blocks of uncompressed data required for compression when writing the next mark. You can also specify this setting in the global settings (see [min_compress_block_size](/docs/en/operations/settings/settings.md/#min-compress-block-size) setting). The value specified when table is created overrides the global value for this setting.
#### max_partitions_to_read
`max_partitions_to_read` — Limits the maximum number of partitions that can be accessed in one query. You can also specify setting [max_partitions_to_read](../../../operations/settings/merge-tree-settings.md#max-partitions-to-read) in the global setting.
`max_partitions_to_read` — Limits the maximum number of partitions that can be accessed in one query. You can also specify setting [max_partitions_to_read](/docs/en/operations/settings/merge-tree-settings.md/#max-partitions-to-read) in the global setting.
**Example of Sections Setting**
@ -184,7 +184,7 @@ ENGINE MergeTree() PARTITION BY toYYYYMM(EventDate) ORDER BY (CounterID, EventDa
In the example, we set partitioning by month.
We also set an expression for sampling as a hash by the user ID. This allows you to pseudorandomize the data in the table for each `CounterID` and `EventDate`. If you define a [SAMPLE](../../../sql-reference/statements/select/sample.md#select-sample-clause) clause when selecting the data, ClickHouse will return an evenly pseudorandom data sample for a subset of users.
We also set an expression for sampling as a hash by the user ID. This allows you to pseudorandomize the data in the table for each `CounterID` and `EventDate`. If you define a [SAMPLE](/docs/en/sql-reference/statements/select/sample.md/#select-sample-clause) clause when selecting the data, ClickHouse will return an evenly pseudorandom data sample for a subset of users.
The `index_granularity` setting can be omitted because 8192 is the default value.
@ -207,9 +207,9 @@ CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster]
**MergeTree() Parameters**
- `date-column` — The name of a column of the [Date](../../../sql-reference/data-types/date.md) type. ClickHouse automatically creates partitions by month based on this column. The partition names are in the `"YYYYMM"` format.
- `date-column` — The name of a column of the [Date](/docs/en/sql-reference/data-types/date.md) type. ClickHouse automatically creates partitions by month based on this column. The partition names are in the `"YYYYMM"` format.
- `sampling_expression` — An expression for sampling.
- `(primary, key)` — Primary key. Type: [Tuple()](../../../sql-reference/data-types/tuple.md)
- `(primary, key)` — Primary key. Type: [Tuple()](/docs/en/sql-reference/data-types/tuple.md)
- `index_granularity` — The granularity of an index. The number of data rows between the “marks” of an index. The value 8192 is appropriate for most tasks.
**Example**
@ -262,7 +262,7 @@ Sparse indexes allow you to work with a very large number of table rows, because
ClickHouse does not require a unique primary key. You can insert multiple rows with the same primary key.
You can use `Nullable`-typed expressions in the `PRIMARY KEY` and `ORDER BY` clauses but it is strongly discouraged. To allow this feature, turn on the [allow_nullable_key](../../../operations/settings/settings.md#allow-nullable-key) setting. The [NULLS_LAST](../../../sql-reference/statements/select/order-by.md#sorting-of-special-values) principle applies for `NULL` values in the `ORDER BY` clause.
You can use `Nullable`-typed expressions in the `PRIMARY KEY` and `ORDER BY` clauses but it is strongly discouraged. To allow this feature, turn on the [allow_nullable_key](/docs/en/operations/settings/settings.md/#allow-nullable-key) setting. The [NULLS_LAST](/docs/en/sql-reference/statements/select/order-by.md/#sorting-of-special-values) principle applies for `NULL` values in the `ORDER BY` clause.
### Selecting the Primary Key {#selecting-the-primary-key}
@ -279,26 +279,26 @@ The number of columns in the primary key is not explicitly limited. Depending on
ClickHouse sorts data by primary key, so the higher the consistency, the better the compression.
- Provide additional logic when merging data parts in the [CollapsingMergeTree](../../../engines/table-engines/mergetree-family/collapsingmergetree.md#table_engine-collapsingmergetree) and [SummingMergeTree](../../../engines/table-engines/mergetree-family/summingmergetree.md) engines.
- Provide additional logic when merging data parts in the [CollapsingMergeTree](/docs/en/engines/table-engines/mergetree-family/collapsingmergetree.md/#table_engine-collapsingmergetree) and [SummingMergeTree](/docs/en/engines/table-engines/mergetree-family/summingmergetree.md) engines.
In this case it makes sense to specify the *sorting key* that is different from the primary key.
A long primary key will negatively affect the insert performance and memory consumption, but extra columns in the primary key do not affect ClickHouse performance during `SELECT` queries.
You can create a table without a primary key using the `ORDER BY tuple()` syntax. In this case, ClickHouse stores data in the order of inserting. If you want to save data order when inserting data by `INSERT ... SELECT` queries, set [max_insert_threads = 1](../../../operations/settings/settings.md#settings-max-insert-threads).
You can create a table without a primary key using the `ORDER BY tuple()` syntax. In this case, ClickHouse stores data in the order of inserting. If you want to save data order when inserting data by `INSERT ... SELECT` queries, set [max_insert_threads = 1](/docs/en/operations/settings/settings.md/#settings-max-insert-threads).
To select data in the initial order, use [single-threaded](../../../operations/settings/settings.md#settings-max_threads) `SELECT` queries.
To select data in the initial order, use [single-threaded](/docs/en/operations/settings/settings.md/#settings-max_threads) `SELECT` queries.
### Choosing a Primary Key that Differs from the Sorting Key {#choosing-a-primary-key-that-differs-from-the-sorting-key}
It is possible to specify a primary key (an expression with values that are written in the index file for each mark) that is different from the sorting key (an expression for sorting the rows in data parts). In this case the primary key expression tuple must be a prefix of the sorting key expression tuple.
This feature is helpful when using the [SummingMergeTree](../../../engines/table-engines/mergetree-family/summingmergetree.md) and
[AggregatingMergeTree](../../../engines/table-engines/mergetree-family/aggregatingmergetree.md) table engines. In a common case when using these engines, the table has two types of columns: *dimensions* and *measures*. Typical queries aggregate values of measure columns with arbitrary `GROUP BY` and filtering by dimensions. Because SummingMergeTree and AggregatingMergeTree aggregate rows with the same value of the sorting key, it is natural to add all dimensions to it. As a result, the key expression consists of a long list of columns and this list must be frequently updated with newly added dimensions.
This feature is helpful when using the [SummingMergeTree](/docs/en/engines/table-engines/mergetree-family/summingmergetree.md) and
[AggregatingMergeTree](/docs/en/engines/table-engines/mergetree-family/aggregatingmergetree.md) table engines. In a common case when using these engines, the table has two types of columns: *dimensions* and *measures*. Typical queries aggregate values of measure columns with arbitrary `GROUP BY` and filtering by dimensions. Because SummingMergeTree and AggregatingMergeTree aggregate rows with the same value of the sorting key, it is natural to add all dimensions to it. As a result, the key expression consists of a long list of columns and this list must be frequently updated with newly added dimensions.
In this case it makes sense to leave only a few columns in the primary key that will provide efficient range scans and add the remaining dimension columns to the sorting key tuple.
[ALTER](../../../sql-reference/statements/alter/index.md) of the sorting key is a lightweight operation because when a new column is simultaneously added to the table and to the sorting key, existing data parts do not need to be changed. Since the old sorting key is a prefix of the new sorting key and there is no data in the newly added column, the data is sorted by both the old and new sorting keys at the moment of table modification.
[ALTER](/docs/en/sql-reference/statements/alter/index.md) of the sorting key is a lightweight operation because when a new column is simultaneously added to the table and to the sorting key, existing data parts do not need to be changed. Since the old sorting key is a prefix of the new sorting key and there is no data in the newly added column, the data is sorted by both the old and new sorting keys at the moment of table modification.
### Use of Indexes and Partitions in Queries {#use-of-indexes-and-partitions-in-queries}
@ -342,7 +342,7 @@ In the example below, the index can’t be used.
SELECT count() FROM table WHERE CounterID = 34 OR URL LIKE '%upyachka%'
```
To check whether ClickHouse can use the index when running a query, use the settings [force_index_by_date](../../../operations/settings/settings.md#settings-force_index_by_date) and [force_primary_key](../../../operations/settings/settings.md#force-primary-key).
To check whether ClickHouse can use the index when running a query, use the settings [force_index_by_date](/docs/en/operations/settings/settings.md/#settings-force_index_by_date) and [force_primary_key](/docs/en/operations/settings/settings.md/#force-primary-key).
The key for partitioning by month allows reading only those data blocks which contain dates from the proper range. In this case, the data block may contain data for many dates (up to an entire month). Within a block, data is sorted by primary key, which might not contain the date as the first column. Because of this, using a query with only a date condition that does not specify the primary key prefix will cause more data to be read than for a single date.
@ -400,7 +400,7 @@ Stores unique values of the specified expression (no more than `max_rows` rows,
#### `ngrambf_v1(n, size_of_bloom_filter_in_bytes, number_of_hash_functions, random_seed)`
Stores a [Bloom filter](https://en.wikipedia.org/wiki/Bloom_filter) that contains all ngrams from a block of data. Works only with datatypes: [String](../../../sql-reference/data-types/string.md), [FixedString](../../../sql-reference/data-types/fixedstring.md) and [Map](../../../sql-reference/data-types/map.md). Can be used for optimization of `EQUALS`, `LIKE` and `IN` expressions.
Stores a [Bloom filter](https://en.wikipedia.org/wiki/Bloom_filter) that contains all ngrams from a block of data. Works only with datatypes: [String](/docs/en/sql-reference/data-types/string.md), [FixedString](/docs/en/sql-reference/data-types/fixedstring.md) and [Map](/docs/en/sql-reference/data-types/map.md). Can be used for optimization of `EQUALS`, `LIKE` and `IN` expressions.
- `n` — ngram size,
- `size_of_bloom_filter_in_bytes` — Bloom filter size in bytes (you can use large values here, for example, 256 or 512, because it can be compressed well).
@ -417,11 +417,11 @@ The optional `false_positive` parameter is the probability of receiving a false
Supported data types: `Int*`, `UInt*`, `Float*`, `Enum`, `Date`, `DateTime`, `String`, `FixedString`, `Array`, `LowCardinality`, `Nullable`, `UUID`, `Map`.
For `Map` data type client can specify if index should be created for keys or values using [mapKeys](../../../sql-reference/functions/tuple-map-functions.md#mapkeys) or [mapValues](../../../sql-reference/functions/tuple-map-functions.md#mapvalues) function.
For `Map` data type client can specify if index should be created for keys or values using [mapKeys](/docs/en/sql-reference/functions/tuple-map-functions.md/#mapkeys) or [mapValues](/docs/en/sql-reference/functions/tuple-map-functions.md/#mapvalues) function.
There are also special-purpose and experimental indexes to support approximate nearest neighbor (ANN) queries. See [here](annindexes.md) for details.
The following functions can use the filter: [equals](../../../sql-reference/functions/comparison-functions.md), [notEquals](../../../sql-reference/functions/comparison-functions.md), [in](../../../sql-reference/functions/in-functions), [notIn](../../../sql-reference/functions/in-functions), [has](../../../sql-reference/functions/array-functions#hasarr-elem), [hasAny](../../../sql-reference/functions/array-functions#hasany), [hasAll](../../../sql-reference/functions/array-functions#hasall).
The following functions can use the filter: [equals](/docs/en/sql-reference/functions/comparison-functions.md), [notEquals](/docs/en/sql-reference/functions/comparison-functions.md), [in](/docs/en/sql-reference/functions/in-functions), [notIn](/docs/en/sql-reference/functions/in-functions), [has](/docs/en/sql-reference/functions/array-functions#hasarr-elem), [hasAny](/docs/en/sql-reference/functions/array-functions#hasany), [hasAll](/docs/en/sql-reference/functions/array-functions#hasall).
Example of index creation for `Map` data type
@ -445,21 +445,21 @@ The `set` index can be used with all functions. Function subsets for other index
| Function (operator) / Index | primary key | minmax | ngrambf_v1 | tokenbf_v1 | bloom_filter |
|------------------------------------------------------------------------------------------------------------|-------------|--------|-------------|-------------|---------------|
| [equals (=, ==)](../../../sql-reference/functions/comparison-functions.md#function-equals) | ✔ | ✔ | ✔ | ✔ | ✔ |
| [notEquals(!=, &lt;&gt;)](../../../sql-reference/functions/comparison-functions.md#function-notequals) | ✔ | ✔ | ✔ | ✔ | ✔ |
| [like](../../../sql-reference/functions/string-search-functions.md#function-like) | ✔ | ✔ | ✔ | ✔ | ✗ |
| [notLike](../../../sql-reference/functions/string-search-functions.md#function-notlike) | ✔ | ✔ | ✔ | ✔ | ✗ |
| [startsWith](../../../sql-reference/functions/string-functions.md#startswith) | ✔ | ✔ | ✔ | ✔ | ✗ |
| [endsWith](../../../sql-reference/functions/string-functions.md#endswith) | ✗ | ✗ | ✔ | ✔ | ✗ |
| [multiSearchAny](../../../sql-reference/functions/string-search-functions.md#function-multisearchany) | ✗ | ✗ | ✔ | ✗ | ✗ |
| [in](../../../sql-reference/functions/in-functions#in-functions) | ✔ | ✔ | ✔ | ✔ | ✔ |
| [notIn](../../../sql-reference/functions/in-functions#in-functions) | ✔ | ✔ | ✔ | ✔ | ✔ |
| [less (<)](../../../sql-reference/functions/comparison-functions.md#function-less) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [greater (>)](../../../sql-reference/functions/comparison-functions.md#function-greater) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [lessOrEquals (<=)](../../../sql-reference/functions/comparison-functions.md#function-lessorequals) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [greaterOrEquals (>=)](../../../sql-reference/functions/comparison-functions.md#function-greaterorequals) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [empty](../../../sql-reference/functions/array-functions#function-empty) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [notEmpty](../../../sql-reference/functions/array-functions#function-notempty) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [equals (=, ==)](/docs/en/sql-reference/functions/comparison-functions.md/#function-equals) | ✔ | ✔ | ✔ | ✔ | ✔ |
| [notEquals(!=, &lt;&gt;)](/docs/en/sql-reference/functions/comparison-functions.md/#function-notequals) | ✔ | ✔ | ✔ | ✔ | ✔ |
| [like](/docs/en/sql-reference/functions/string-search-functions.md/#function-like) | ✔ | ✔ | ✔ | ✔ | ✗ |
| [notLike](/docs/en/sql-reference/functions/string-search-functions.md/#function-notlike) | ✔ | ✔ | ✔ | ✔ | ✗ |
| [startsWith](/docs/en/sql-reference/functions/string-functions.md/#startswith) | ✔ | ✔ | ✔ | ✔ | ✗ |
| [endsWith](/docs/en/sql-reference/functions/string-functions.md/#endswith) | ✗ | ✗ | ✔ | ✔ | ✗ |
| [multiSearchAny](/docs/en/sql-reference/functions/string-search-functions.md/#function-multisearchany) | ✗ | ✗ | ✔ | ✗ | ✗ |
| [in](/docs/en/sql-reference/functions/in-functions#in-functions) | ✔ | ✔ | ✔ | ✔ | ✔ |
| [notIn](/docs/en/sql-reference/functions/in-functions#in-functions) | ✔ | ✔ | ✔ | ✔ | ✔ |
| [less (<)](/docs/en/sql-reference/functions/comparison-functions.md/#function-less) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [greater (>)](/docs/en/sql-reference/functions/comparison-functions.md/#function-greater) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [lessOrEquals (<=)](/docs/en/sql-reference/functions/comparison-functions.md/#function-lessorequals) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [greaterOrEquals (>=)](/docs/en/sql-reference/functions/comparison-functions.md/#function-greaterorequals) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [empty](/docs/en/sql-reference/functions/array-functions#function-empty) | ✔ | ✔ | ✗ | ✗ | ✗ |
| [notEmpty](/docs/en/sql-reference/functions/array-functions#function-notempty) | ✔ | ✔ | ✗ | ✗ | ✗ |
| hasToken | ✗ | ✗ | ✗ | ✔ | ✗ |
Functions with a constant argument that is less than ngram size can’t be used by `ngrambf_v1` for query optimization.
@ -485,16 +485,16 @@ For example:
## Approximate Nearest Neighbor Search Indexes [experimental] {#table_engines-ANNIndex}
In addition to skip indices, there are also [Approximate Nearest Neighbor Search Indexes](../../../engines/table-engines/mergetree-family/annindexes.md).
In addition to skip indices, there are also [Approximate Nearest Neighbor Search Indexes](/docs/en/engines/table-engines/mergetree-family/annindexes.md).
## Projections {#projections}
Projections are like [materialized views](../../../sql-reference/statements/create/view.md#materialized) but defined in part-level. It provides consistency guarantees along with automatic usage in queries.
Projections are like [materialized views](/docs/en/sql-reference/statements/create/view.md/#materialized) but defined in part-level. It provides consistency guarantees along with automatic usage in queries.
:::note
When you are implementing projections you should also consider the [force_optimize_projection](../../../operations/settings/settings.md#force-optimize-projection) setting.
When you are implementing projections you should also consider the [force_optimize_projection](/docs/en/operations/settings/settings.md/#force-optimize-projection) setting.
:::
Projections are not supported in the `SELECT` statements with the [FINAL](../../../sql-reference/statements/select/from.md#select-from-final) modifier.
Projections are not supported in the `SELECT` statements with the [FINAL](/docs/en/sql-reference/statements/select/from.md/#select-from-final) modifier.
### Projection Query {#projection-query}
A projection query is what defines a projection. It implicitly selects data from the parent table.
@ -504,7 +504,7 @@ A projection query is what defines a projection. It implicitly selects data from
SELECT <column list expr> [GROUP BY] <group keys expr> [ORDER BY] <expr>
```
Projections can be modified or dropped with the [ALTER](../../../sql-reference/statements/alter/projection.md) statement.
Projections can be modified or dropped with the [ALTER](/docs/en/sql-reference/statements/alter/projection.md) statement.
### Projection Storage {#projection-storage}
Projections are stored inside the part directory. It's similar to an index but contains a subdirectory that stores an anonymous `MergeTree` table's part. The table is induced by the definition query of the projection. If there is a `GROUP BY` clause, the underlying storage engine becomes [AggregatingMergeTree](aggregatingmergetree.md), and all aggregate functions are converted to `AggregateFunction`. If there is an `ORDER BY` clause, the `MergeTree` table uses it as its primary key expression. During the merge process the projection part is merged via its storage's merge routine. The checksum of the parent table's part is combined with the projection's part. Other maintenance jobs are similar to skip indices.
@ -526,7 +526,7 @@ Determines the lifetime of values.
The `TTL` clause can be set for the whole table and for each individual column. Table-level `TTL` can also specify the logic of automatic moving data between disks and volumes, or recompressing parts where all the data has been expired.
Expressions must evaluate to [Date](../../../sql-reference/data-types/date.md) or [DateTime](../../../sql-reference/data-types/datetime.md) data type.
Expressions must evaluate to [Date](/docs/en/sql-reference/data-types/date.md) or [DateTime](/docs/en/sql-reference/data-types/datetime.md) data type.
**Syntax**
@ -537,7 +537,7 @@ TTL time_column
TTL time_column + interval
```
To define `interval`, use [time interval](../../../sql-reference/operators/index.md#operators-datetime) operators, for example:
To define `interval`, use [time interval](/docs/en/sql-reference/operators/index.md/#operators-datetime) operators, for example:
``` sql
TTL date_time + INTERVAL 1 MONTH
@ -684,11 +684,11 @@ Data with an expired `TTL` is removed when ClickHouse merges data parts.
When ClickHouse detects that data is expired, it performs an off-schedule merge. To control the frequency of such merges, you can set `merge_with_ttl_timeout`. If the value is too low, it will perform many off-schedule merges that may consume a lot of resources.
If you perform the `SELECT` query between merges, you may get expired data. To avoid it, use the [OPTIMIZE](../../../sql-reference/statements/optimize.md) query before `SELECT`.
If you perform the `SELECT` query between merges, you may get expired data. To avoid it, use the [OPTIMIZE](/docs/en/sql-reference/statements/optimize.md) query before `SELECT`.
**See Also**
- [ttl_only_drop_parts](../../../operations/settings/settings.md#ttl_only_drop_parts) setting
- [ttl_only_drop_parts](/docs/en/operations/settings/settings.md/#ttl_only_drop_parts) setting
## Using Multiple Block Devices for Data Storage {#table_engine-mergetree-multiple-volumes}
@ -697,16 +697,16 @@ If you perform the `SELECT` query between merges, you may get expired data. To a
`MergeTree` family table engines can store data on multiple block devices. For example, it can be useful when the data of a certain table are implicitly split into “hot” and “cold”. The most recent data is regularly requested but requires only a small amount of space. On the contrary, the fat-tailed historical data is requested rarely. If several disks are available, the “hot” data may be located on fast disks (for example, NVMe SSDs or in memory), while the “cold” data - on relatively slow ones (for example, HDD).
Data part is the minimum movable unit for `MergeTree`-engine tables. The data belonging to one part are stored on one disk. Data parts can be moved between disks in the background (according to user settings) as well as by means of the [ALTER](../../../sql-reference/statements/alter/partition.md#alter_move-partition) queries.
Data part is the minimum movable unit for `MergeTree`-engine tables. The data belonging to one part are stored on one disk. Data parts can be moved between disks in the background (according to user settings) as well as by means of the [ALTER](/docs/en/sql-reference/statements/alter/partition.md/#alter_move-partition) queries.
### Terms {#terms}
- Disk — Block device mounted to the filesystem.
- Default disk — Disk that stores the path specified in the [path](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-path) server setting.
- Default disk — Disk that stores the path specified in the [path](/docs/en/operations/server-configuration-parameters/settings.md/#server_configuration_parameters-path) server setting.
- Volume — Ordered set of equal disks (similar to [JBOD](https://en.wikipedia.org/wiki/Non-RAID_drive_architectures)).
- Storage policy — Set of volumes and the rules for moving data between them.
The names given to the described entities can be found in the system tables, [system.storage_policies](../../../operations/system-tables/storage_policies.md#system_tables-storage_policies) and [system.disks](../../../operations/system-tables/disks.md#system_tables-disks). To apply one of the configured storage policies for a table, use the `storage_policy` setting of `MergeTree`-engine family tables.
The names given to the described entities can be found in the system tables, [system.storage_policies](/docs/en/operations/system-tables/storage_policies.md/#system_tables-storage_policies) and [system.disks](/docs/en/operations/system-tables/disks.md/#system_tables-disks). To apply one of the configured storage policies for a table, use the `storage_policy` setting of `MergeTree`-engine family tables.
### Configuration {#table_engine-mergetree-multiple-volumes_configure}
@ -853,16 +853,16 @@ SETTINGS storage_policy = 'moving_from_ssd_to_hdd'
The `default` storage policy implies using only one volume, which consists of only one disk given in `<path>`.
You could change storage policy after table creation with [ALTER TABLE ... MODIFY SETTING] query, new policy should include all old disks and volumes with same names.
The number of threads performing background moves of data parts can be changed by [background_move_pool_size](../../../operations/settings/settings.md#background_move_pool_size) setting.
The number of threads performing background moves of data parts can be changed by [background_move_pool_size](/docs/en/operations/settings/settings.md/#background_move_pool_size) setting.
### Details {#details}
In the case of `MergeTree` tables, data is getting to disk in different ways:
- As a result of an insert (`INSERT` query).
- During background merges and [mutations](../../../sql-reference/statements/alter/index.md#alter-mutations).
- During background merges and [mutations](/docs/en/sql-reference/statements/alter/index.md/#alter-mutations).
- When downloading from another replica.
- As a result of partition freezing [ALTER TABLE … FREEZE PARTITION](../../../sql-reference/statements/alter/partition.md#alter_freeze-partition).
- As a result of partition freezing [ALTER TABLE … FREEZE PARTITION](/docs/en/sql-reference/statements/alter/partition.md/#alter_freeze-partition).
In all these cases except for mutations and partition freezing, a part is stored on a volume and a disk according to the given storage policy:
@ -872,16 +872,16 @@ In all these cases except for mutations and partition freezing, a part is stored
Under the hood, mutations and partition freezing make use of [hard links](https://en.wikipedia.org/wiki/Hard_link). Hard links between different disks are not supported, therefore in such cases the resulting parts are stored on the same disks as the initial ones.
In the background, parts are moved between volumes on the basis of the amount of free space (`move_factor` parameter) according to the order the volumes are declared in the configuration file.
Data is never transferred from the last one and into the first one. One may use system tables [system.part_log](../../../operations/system-tables/part_log.md#system_tables-part-log) (field `type = MOVE_PART`) and [system.parts](../../../operations/system-tables/parts.md#system_tables-parts) (fields `path` and `disk`) to monitor background moves. Also, the detailed information can be found in server logs.
Data is never transferred from the last one and into the first one. One may use system tables [system.part_log](/docs/en/operations/system-tables/part_log.md/#system_tables-part-log) (field `type = MOVE_PART`) and [system.parts](/docs/en/operations/system-tables/parts.md/#system_tables-parts) (fields `path` and `disk`) to monitor background moves. Also, the detailed information can be found in server logs.
User can force moving a part or a partition from one volume to another using the query [ALTER TABLE … MOVE PART\|PARTITION … TO VOLUME\|DISK …](../../../sql-reference/statements/alter/partition.md#alter_move-partition), all the restrictions for background operations are taken into account. The query initiates a move on its own and does not wait for background operations to be completed. User will get an error message if not enough free space is available or if any of the required conditions are not met.
User can force moving a part or a partition from one volume to another using the query [ALTER TABLE … MOVE PART\|PARTITION … TO VOLUME\|DISK …](/docs/en/sql-reference/statements/alter/partition.md/#alter_move-partition), all the restrictions for background operations are taken into account. The query initiates a move on its own and does not wait for background operations to be completed. User will get an error message if not enough free space is available or if any of the required conditions are not met.
Moving data does not interfere with data replication. Therefore, different storage policies can be specified for the same table on different replicas.
After the completion of background merges and mutations, old parts are removed only after a certain amount of time (`old_parts_lifetime`).
During this time, they are not moved to other volumes or disks. Therefore, until the parts are finally removed, they are still taken into account for evaluation of the occupied disk space.
User can assign new big parts to different disks of a [JBOD](https://en.wikipedia.org/wiki/Non-RAID_drive_architectures) volume in a balanced way using the [min_bytes_to_rebalance_partition_over_jbod](../../../operations/settings/merge-tree-settings.md#min-bytes-to-rebalance-partition-over-jbod) setting.
User can assign new big parts to different disks of a [JBOD](https://en.wikipedia.org/wiki/Non-RAID_drive_architectures) volume in a balanced way using the [min_bytes_to_rebalance_partition_over_jbod](/docs/en/operations/settings/merge-tree-settings.md/#min-bytes-to-rebalance-partition-over-jbod) setting.
## Using S3 for Data Storage {#table_engine-mergetree-s3}

26
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@ -20,7 +20,7 @@ Replication works at the level of an individual table, not the entire server. A
Replication does not depend on sharding. Each shard has its own independent replication.
Compressed data for `INSERT` and `ALTER` queries is replicated (for more information, see the documentation for [ALTER](../../../sql-reference/statements/alter/index.md#query_language_queries_alter)).
Compressed data for `INSERT` and `ALTER` queries is replicated (for more information, see the documentation for [ALTER](/docs/en/sql-reference/statements/alter/index.md/#query_language_queries_alter)).
`CREATE`, `DROP`, `ATTACH`, `DETACH` and `RENAME` queries are executed on a single server and are not replicated:
@ -28,9 +28,9 @@ Compressed data for `INSERT` and `ALTER` queries is replicated (for more informa
- The `DROP TABLE` query deletes the replica located on the server where the query is run.
- The `RENAME` query renames the table on one of the replicas. In other words, replicated tables can have different names on different replicas.
ClickHouse uses [ClickHouse Keeper](../../../guides/sre/keeper/clickhouse-keeper.md) for storing replicas meta information. It is possible to use ZooKeeper version 3.4.5 or newer, but ClickHouse Keeper is recommended.
ClickHouse uses [ClickHouse Keeper](/docs/en/guides/sre/keeper/clickhouse-keeper.md) for storing replicas meta information. It is possible to use ZooKeeper version 3.4.5 or newer, but ClickHouse Keeper is recommended.
To use replication, set parameters in the [zookeeper](../../../operations/server-configuration-parameters/settings.md#server-settings_zookeeper) server configuration section.
To use replication, set parameters in the [zookeeper](/docs/en/operations/server-configuration-parameters/settings.md/#server-settings_zookeeper) server configuration section.
:::warning
Don’t neglect the security setting. ClickHouse supports the `digest` [ACL scheme](https://zookeeper.apache.org/doc/current/zookeeperProgrammers.html#sc_ZooKeeperAccessControl) of the ZooKeeper security subsystem.
@ -95,21 +95,21 @@ You can specify any existing ZooKeeper cluster and the system will use a directo
If ZooKeeper isn’t set in the config file, you can’t create replicated tables, and any existing replicated tables will be read-only.
ZooKeeper is not used in `SELECT` queries because replication does not affect the performance of `SELECT` and queries run just as fast as they do for non-replicated tables. When querying distributed replicated tables, ClickHouse behavior is controlled by the settings [max_replica_delay_for_distributed_queries](../../../operations/settings/settings.md#settings-max_replica_delay_for_distributed_queries) and [fallback_to_stale_replicas_for_distributed_queries](../../../operations/settings/settings.md#settings-fallback_to_stale_replicas_for_distributed_queries).
ZooKeeper is not used in `SELECT` queries because replication does not affect the performance of `SELECT` and queries run just as fast as they do for non-replicated tables. When querying distributed replicated tables, ClickHouse behavior is controlled by the settings [max_replica_delay_for_distributed_queries](/docs/en/operations/settings/settings.md/#settings-max_replica_delay_for_distributed_queries) and [fallback_to_stale_replicas_for_distributed_queries](/docs/en/operations/settings/settings.md/#settings-fallback_to_stale_replicas_for_distributed_queries).
For each `INSERT` query, approximately ten entries are added to ZooKeeper through several transactions. (To be more precise, this is for each inserted block of data; an INSERT query contains one block or one block per `max_insert_block_size = 1048576` rows.) This leads to slightly longer latencies for `INSERT` compared to non-replicated tables. But if you follow the recommendations to insert data in batches of no more than one `INSERT` per second, it does not create any problems. The entire ClickHouse cluster used for coordinating one ZooKeeper cluster has a total of several hundred `INSERTs` per second. The throughput on data inserts (the number of rows per second) is just as high as for non-replicated data.
For very large clusters, you can use different ZooKeeper clusters for different shards. However, from our experience this has not proven necessary based on production clusters with approximately 300 servers.
Replication is asynchronous and multi-master. `INSERT` queries (as well as `ALTER`) can be sent to any available server. Data is inserted on the server where the query is run, and then it is copied to the other servers. Because it is asynchronous, recently inserted data appears on the other replicas with some latency. If part of the replicas are not available, the data is written when they become available. If a replica is available, the latency is the amount of time it takes to transfer the block of compressed data over the network. The number of threads performing background tasks for replicated tables can be set by [background_schedule_pool_size](../../../operations/settings/settings.md#background_schedule_pool_size) setting.
Replication is asynchronous and multi-master. `INSERT` queries (as well as `ALTER`) can be sent to any available server. Data is inserted on the server where the query is run, and then it is copied to the other servers. Because it is asynchronous, recently inserted data appears on the other replicas with some latency. If part of the replicas are not available, the data is written when they become available. If a replica is available, the latency is the amount of time it takes to transfer the block of compressed data over the network. The number of threads performing background tasks for replicated tables can be set by [background_schedule_pool_size](/docs/en/operations/settings/settings.md/#background_schedule_pool_size) setting.
`ReplicatedMergeTree` engine uses a separate thread pool for replicated fetches. Size of the pool is limited by the [background_fetches_pool_size](../../../operations/settings/settings.md#background_fetches_pool_size) setting which can be tuned with a server restart.
`ReplicatedMergeTree` engine uses a separate thread pool for replicated fetches. Size of the pool is limited by the [background_fetches_pool_size](/docs/en/operations/settings/settings.md/#background_fetches_pool_size) setting which can be tuned with a server restart.
By default, an INSERT query waits for confirmation of writing the data from only one replica. If the data was successfully written to only one replica and the server with this replica ceases to exist, the stored data will be lost. To enable getting confirmation of data writes from multiple replicas, use the `insert_quorum` option.
Each block of data is written atomically. The INSERT query is divided into blocks up to `max_insert_block_size = 1048576` rows. In other words, if the `INSERT` query has less than 1048576 rows, it is made atomically.
Data blocks are deduplicated. For multiple writes of the same data block (data blocks of the same size containing the same rows in the same order), the block is only written once. The reason for this is in case of network failures when the client application does not know if the data was written to the DB, so the `INSERT` query can simply be repeated. It does not matter which replica INSERTs were sent to with identical data. `INSERTs` are idempotent. Deduplication parameters are controlled by [merge_tree](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-merge_tree) server settings.
Data blocks are deduplicated. For multiple writes of the same data block (data blocks of the same size containing the same rows in the same order), the block is only written once. The reason for this is in case of network failures when the client application does not know if the data was written to the DB, so the `INSERT` query can simply be repeated. It does not matter which replica INSERTs were sent to with identical data. `INSERTs` are idempotent. Deduplication parameters are controlled by [merge_tree](/docs/en/operations/server-configuration-parameters/settings.md/#server_configuration_parameters-merge_tree) server settings.
During replication, only the source data to insert is transferred over the network. Further data transformation (merging) is coordinated and performed on all the replicas in the same way. This minimizes network usage, which means that replication works well when replicas reside in different datacenters. (Note that duplicating data in different datacenters is the main goal of replication.)
@ -165,7 +165,7 @@ CREATE TABLE table_name
</details>
As the example shows, these parameters can contain substitutions in curly brackets. The substituted values are taken from the [macros](../../../operations/server-configuration-parameters/settings.md#macros) section of the configuration file.
As the example shows, these parameters can contain substitutions in curly brackets. The substituted values are taken from the [macros](/docs/en/operations/server-configuration-parameters/settings.md/#macros) section of the configuration file.
Example:
@ -295,10 +295,10 @@ If the data in ClickHouse Keeper was lost or damaged, you can save data by movin
**See Also**
- [background_schedule_pool_size](../../../operations/settings/settings.md#background_schedule_pool_size)
- [background_fetches_pool_size](../../../operations/settings/settings.md#background_fetches_pool_size)
- [execute_merges_on_single_replica_time_threshold](../../../operations/settings/settings.md#execute-merges-on-single-replica-time-threshold)
- [max_replicated_fetches_network_bandwidth](../../../operations/settings/merge-tree-settings.md#max_replicated_fetches_network_bandwidth)
- [max_replicated_sends_network_bandwidth](../../../operations/settings/merge-tree-settings.md#max_replicated_sends_network_bandwidth)
- [background_schedule_pool_size](/docs/en/operations/settings/settings.md/#background_schedule_pool_size)
- [background_fetches_pool_size](/docs/en/operations/settings/settings.md/#background_fetches_pool_size)
- [execute_merges_on_single_replica_time_threshold](/docs/en/operations/settings/settings.md/#execute-merges-on-single-replica-time-threshold)
- [max_replicated_fetches_network_bandwidth](/docs/en/operations/settings/merge-tree-settings.md/#max_replicated_fetches_network_bandwidth)
- [max_replicated_sends_network_bandwidth](/docs/en/operations/settings/merge-tree-settings.md/#max_replicated_sends_network_bandwidth)
[Original article](https://clickhouse.com/docs/en/operations/table_engines/replication/) <!--hide-->

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@ -6,10 +6,10 @@ sidebar_label: Join
# Join Table Engine
Optional prepared data structure for usage in [JOIN](../../../sql-reference/statements/select/join.md#select-join) operations.
Optional prepared data structure for usage in [JOIN](/docs/en/sql-reference/statements/select/join.md/#select-join) operations.
:::note
This is not an article about the [JOIN clause](../../../sql-reference/statements/select/join.md#select-join) itself.
This is not an article about the [JOIN clause](/docs/en/sql-reference/statements/select/join.md/#select-join) itself.
:::
## Creating a Table {#creating-a-table}
@ -22,17 +22,17 @@ CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster]
) ENGINE = Join(join_strictness, join_type, k1[, k2, ...])
```
See the detailed description of the [CREATE TABLE](../../../sql-reference/statements/create/table.md#create-table-query) query.
See the detailed description of the [CREATE TABLE](/docs/en/sql-reference/statements/create/table.md/#create-table-query) query.
## Engine Parameters
### join_strictness
`join_strictness` – [JOIN strictness](../../../sql-reference/statements/select/join.md#select-join-types).
`join_strictness` – [JOIN strictness](/docs/en/sql-reference/statements/select/join.md/#select-join-types).
### join_type
`join_type` – [JOIN type](../../../sql-reference/statements/select/join.md#select-join-types).
`join_type` – [JOIN type](/docs/en/sql-reference/statements/select/join.md/#select-join-types).
### Key columns
@ -55,11 +55,11 @@ You can use `INSERT` queries to add data to the `Join`-engine tables. If the tab
Main use-cases for `Join`-engine tables are following:
- Place the table to the right side in a `JOIN` clause.
- Call the [joinGet](../../../sql-reference/functions/other-functions.md#joinget) function, which lets you extract data from the table the same way as from a dictionary.
- Call the [joinGet](/docs/en/sql-reference/functions/other-functions.md/#joinget) function, which lets you extract data from the table the same way as from a dictionary.
### Deleting Data {#deleting-data}
`ALTER DELETE` queries for `Join`-engine tables are implemented as [mutations](../../../sql-reference/statements/alter/index.md#mutations). `DELETE` mutation reads filtered data and overwrites data of memory and disk.
`ALTER DELETE` queries for `Join`-engine tables are implemented as [mutations](/docs/en/sql-reference/statements/alter/index.md/#mutations). `DELETE` mutation reads filtered data and overwrites data of memory and disk.
### Limitations and Settings {#join-limitations-and-settings}
@ -67,30 +67,30 @@ When creating a table, the following settings are applied:
#### join_use_nulls
[join_use_nulls](../../../operations/settings/settings.md#join_use_nulls)
[join_use_nulls](/docs/en/operations/settings/settings.md/#join_use_nulls)
#### max_rows_in_join
[max_rows_in_join](../../../operations/settings/query-complexity.md#settings-max_rows_in_join)
[max_rows_in_join](/docs/en/operations/settings/query-complexity.md/#settings-max_rows_in_join)
#### max_bytes_in_join
[max_bytes_in_join](../../../operations/settings/query-complexity.md#settings-max_bytes_in_join)
[max_bytes_in_join](/docs/en/operations/settings/query-complexity.md/#settings-max_bytes_in_join)
#### join_overflow_mode
[join_overflow_mode](../../../operations/settings/query-complexity.md#settings-join_overflow_mode)
[join_overflow_mode](/docs/en/operations/settings/query-complexity.md/#settings-join_overflow_mode)
#### join_any_take_last_row
[join_any_take_last_row](../../../operations/settings/settings.md#settings-join_any_take_last_row)
[join_any_take_last_row](/docs/en/operations/settings/settings.md/#settings-join_any_take_last_row)
#### join_use_nulls
[persistent](../../../operations/settings/settings.md#persistent)
[persistent](/docs/en/operations/settings/settings.md/#persistent)
The `Join`-engine tables can’t be used in `GLOBAL JOIN` operations.
The `Join`-engine allows to specify [join_use_nulls](../../../operations/settings/settings.md#join_use_nulls) setting in the `CREATE TABLE` statement. [SELECT](../../../sql-reference/statements/select/index.md) query should have the same `join_use_nulls` value.
The `Join`-engine allows to specify [join_use_nulls](/docs/en/operations/settings/settings.md/#join_use_nulls) setting in the `CREATE TABLE` statement. [SELECT](/docs/en/sql-reference/statements/select/index.md) query should have the same `join_use_nulls` value.
## Usage Examples {#example}

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@ -163,7 +163,7 @@ SELECT mcc, count() FROM cell_towers GROUP BY mcc ORDER BY count() DESC LIMIT 10
Based on the above query and the [MCC list](https://en.wikipedia.org/wiki/Mobile_country_code), the countries with the most cell towers are: the USA, Germany, and Russia.
You may want to create an [External Dictionary](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md) in ClickHouse to decode these values.
You may want to create a [Dictionary](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md) in ClickHouse to decode these values.
## Use case: Incorporate geo data {#use-case}

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@ -5,7 +5,7 @@ sidebar_label: Input and Output Formats
title: Formats for Input and Output Data
---
ClickHouse can accept and return data in various formats. A format supported for input can be used to parse the data provided to `INSERT`s, to perform `SELECT`s from a file-backed table such as File, URL or HDFS, or to read an external dictionary. A format supported for output can be used to arrange the
ClickHouse can accept and return data in various formats. A format supported for input can be used to parse the data provided to `INSERT`s, to perform `SELECT`s from a file-backed table such as File, URL or HDFS, or to read a dictionary. A format supported for output can be used to arrange the
results of a `SELECT`, and to perform `INSERT`s into a file-backed table.
The supported formats are:

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@ -130,7 +130,7 @@ SHOW TABLES FROM mydatabase;
└────────┘
```
### Example of using named collections with an external dictionary with source MySQL
### Example of using named collections with a dictionary with source MySQL
```sql
CREATE DICTIONARY dict (A Int64, B String)
@ -213,7 +213,7 @@ SHOW TABLES FROM mydatabase
└──────┘
```
### Example of using named collections with an external dictionary with source POSTGRESQL
### Example of using named collections with a dictionary with source POSTGRESQL
```sql
CREATE DICTIONARY dict (a Int64, b String)
@ -270,7 +270,7 @@ SELECT * FROM remote(remote1, database = default, table = test);
└───┴───┘
```
### Example of using named collections with an external dictionary with source ClickHouse
### Example of using named collections with a dictionary with source ClickHouse
```sql
CREATE DICTIONARY dict(a Int64, b String)

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@ -268,14 +268,14 @@ The path to the table in ZooKeeper.
## dictionaries_config {#server_configuration_parameters-dictionaries_config}
The path to the config file for external dictionaries.
The path to the config file for dictionaries.
Path:
- Specify the absolute path or the path relative to the server config file.
- The path can contain wildcards \* and ?.
See also “[External dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md)”.
See also “[Dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md)”.
**Example**

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@ -16,44 +16,54 @@ Queries in ClickHouse can be divided into several types:
The following settings regulate user permissions by the type of query:
- [readonly](#settings_readonly) — Restricts permissions for all types of queries except DDL queries.
- [allow_ddl](#settings_allow_ddl) — Restricts permissions for DDL queries.
## readonly
Restricts permissions for read data, write data, and change settings queries.
`KILL QUERY` can be performed with any settings.
When set to 1, allows:
## readonly {#settings_readonly}
- All types of read queries (like SELECT and equivalent queries).
- Queries that modify only session context (like USE).
Restricts permissions for reading data, write data and change settings queries.
When set to 2, allows the above plus:
- SET and CREATE TEMPORARY TABLE
See how the queries are divided into types [above](#permissions_for_queries).
:::tip
Queries like EXISTS, DESCRIBE, EXPLAIN, SHOW PROCESSLIST, etc are equivalent to SELECT, because they just do select from system tables.
:::
Possible values:
- 0 — All queries are allowed.
- 1 — Only read data queries are allowed.
- 2 — Read data and change settings queries are allowed.
- 0 — Read, Write, and Change settings queries are allowed.
- 1 — Only Read data queries are allowed.
- 2 — Read data and Change settings queries are allowed.
Default value: 0
:::note
After setting `readonly = 1`, the user can’t change `readonly` and `allow_ddl` settings in the current session.
When using the `GET` method in the [HTTP interface](../../interfaces/http.md), `readonly = 1` is set automatically. To modify data, use the `POST` method.
Setting `readonly = 1` prohibit the user from changing all the settings. There is a way to prohibit the user from changing only specific settings. Also there is a way to allow changing only specific settings under `readonly = 1` restrictions. For details see [constraints on settings](../../operations/settings/constraints-on-settings.md).
Setting `readonly = 1` prohibits the user from changing settings. There is a way to prohibit the user from changing only specific settings. Also there is a way to allow changing only specific settings under `readonly = 1` restrictions. For details see [constraints on settings](../../operations/settings/constraints-on-settings.md).
:::
Default value: 0
## allow_ddl {#settings_allow_ddl}
Allows or denies [DDL](https://en.wikipedia.org/wiki/Data_definition_language) queries.
See how the queries are divided into types [above](#permissions_for_queries).
Possible values:
- 0 — DDL queries are not allowed.
- 1 — DDL queries are allowed.
You can’t execute `SET allow_ddl = 1` if `allow_ddl = 0` for the current session.
Default value: 1
[Original article](https://clickhouse.com/docs/en/operations/settings/permissions_for_queries/) <!--hide-->
:::note
You cannot run `SET allow_ddl = 1` if `allow_ddl = 0` for the current session.
:::
:::note KILL QUERY
`KILL QUERY` can be performed with any combination of readonly and allow_ddl settings.
:::

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@ -70,7 +70,7 @@ Another use case of `prefer_global_in_and_join` is accessing tables created by
**See also:**
- [Distributed subqueries](../../sql-reference/operators/in.md#select-distributed-subqueries) for more information on how to use `GLOBAL IN`/`GLOBAL JOIN`
- [Distributed subqueries](../../sql-reference/operators/in.md/#select-distributed-subqueries) for more information on how to use `GLOBAL IN`/`GLOBAL JOIN`
## enable_optimize_predicate_expression {#enable-optimize-predicate-expression}
@ -170,7 +170,7 @@ It makes sense to disable it if the server has millions of tiny tables that are
## function_range_max_elements_in_block {#settings-function_range_max_elements_in_block}
Sets the safety threshold for data volume generated by function [range](../../sql-reference/functions/array-functions.md#range). Defines the maximum number of values generated by function per block of data (sum of array sizes for every row in a block).
Sets the safety threshold for data volume generated by function [range](../../sql-reference/functions/array-functions.md/#range). Defines the maximum number of values generated by function per block of data (sum of array sizes for every row in a block).
Possible values:
@ -273,10 +273,10 @@ Default value: 0.
## insert_null_as_default {#insert_null_as_default}
Enables or disables the insertion of [default values](../../sql-reference/statements/create/table.md#create-default-values) instead of [NULL](../../sql-reference/syntax.md#null-literal) into columns with not [nullable](../../sql-reference/data-types/nullable.md#data_type-nullable) data type.
Enables or disables the insertion of [default values](../../sql-reference/statements/create/table.md/#create-default-values) instead of [NULL](../../sql-reference/syntax.md/#null-literal) into columns with not [nullable](../../sql-reference/data-types/nullable.md/#data_type-nullable) data type.
If column type is not nullable and this setting is disabled, then inserting `NULL` causes an exception. If column type is nullable, then `NULL` values are inserted as is, regardless of this setting.
This setting is applicable to [INSERT ... SELECT](../../sql-reference/statements/insert-into.md#insert_query_insert-select) queries. Note that `SELECT` subqueries may be concatenated with `UNION ALL` clause.
This setting is applicable to [INSERT ... SELECT](../../sql-reference/statements/insert-into.md/#insert_query_insert-select) queries. Note that `SELECT` subqueries may be concatenated with `UNION ALL` clause.
Possible values:
@ -287,7 +287,7 @@ Default value: `1`.
## join_default_strictness {#settings-join_default_strictness}
Sets default strictness for [JOIN clauses](../../sql-reference/statements/select/join.md#select-join).
Sets default strictness for [JOIN clauses](../../sql-reference/statements/select/join.md/#select-join).
Possible values:
@ -322,7 +322,7 @@ When using `partial_merge` algorithm, ClickHouse sorts the data and dumps it to
- `direct` - can be applied when the right storage supports key-value requests.
The `direct` algorithm performs a lookup in the right table using rows from the left table as keys. It's supported only by special storage such as [Dictionary](../../engines/table-engines/special/dictionary.md#dictionary) or [EmbeddedRocksDB](../../engines/table-engines/integrations/embedded-rocksdb.md) and only the `LEFT` and `INNER` JOINs.
The `direct` algorithm performs a lookup in the right table using rows from the left table as keys. It's supported only by special storage such as [Dictionary](../../engines/table-engines/special/dictionary.md/#dictionary) or [EmbeddedRocksDB](../../engines/table-engines/integrations/embedded-rocksdb.md) and only the `LEFT` and `INNER` JOINs.
- `auto` — try `hash` join and switch on the fly to another algorithm if the memory limit is violated.
@ -348,7 +348,7 @@ Default value: 0.
See also:
- [JOIN clause](../../sql-reference/statements/select/join.md#select-join)
- [JOIN clause](../../sql-reference/statements/select/join.md/#select-join)
- [Join table engine](../../engines/table-engines/special/join.md)
- [join_default_strictness](#settings-join_default_strictness)
@ -359,7 +359,7 @@ Sets the type of [JOIN](../../sql-reference/statements/select/join.md) behaviour
Possible values:
- 0 — The empty cells are filled with the default value of the corresponding field type.
- 1 — `JOIN` behaves the same way as in standard SQL. The type of the corresponding field is converted to [Nullable](../../sql-reference/data-types/nullable.md#data_type-nullable), and empty cells are filled with [NULL](../../sql-reference/syntax.md).
- 1 — `JOIN` behaves the same way as in standard SQL. The type of the corresponding field is converted to [Nullable](../../sql-reference/data-types/nullable.md/#data_type-nullable), and empty cells are filled with [NULL](../../sql-reference/syntax.md).
Default value: 0.
@ -431,7 +431,7 @@ Default value: 0.
See also:
- [JOIN strictness](../../sql-reference/statements/select/join.md#join-settings)
- [JOIN strictness](../../sql-reference/statements/select/join.md/#join-settings)
## temporary_files_codec {#temporary_files_codec}
@ -532,7 +532,7 @@ Default value: 8.
If ClickHouse should read more than `merge_tree_max_rows_to_use_cache` rows in one query, it does not use the cache of uncompressed blocks.
The cache of uncompressed blocks stores data extracted for queries. ClickHouse uses this cache to speed up responses to repeated small queries. This setting protects the cache from trashing by queries that read a large amount of data. The [uncompressed_cache_size](../../operations/server-configuration-parameters/settings.md#server-settings-uncompressed_cache_size) server setting defines the size of the cache of uncompressed blocks.
The cache of uncompressed blocks stores data extracted for queries. ClickHouse uses this cache to speed up responses to repeated small queries. This setting protects the cache from trashing by queries that read a large amount of data. The [uncompressed_cache_size](../../operations/server-configuration-parameters/settings.md/#server-settings-uncompressed_cache_size) server setting defines the size of the cache of uncompressed blocks.
Possible values:
@ -544,7 +544,7 @@ Default value: 128 ✕ 8192.
If ClickHouse should read more than `merge_tree_max_bytes_to_use_cache` bytes in one query, it does not use the cache of uncompressed blocks.
The cache of uncompressed blocks stores data extracted for queries. ClickHouse uses this cache to speed up responses to repeated small queries. This setting protects the cache from trashing by queries that read a large amount of data. The [uncompressed_cache_size](../../operations/server-configuration-parameters/settings.md#server-settings-uncompressed_cache_size) server setting defines the size of the cache of uncompressed blocks.
The cache of uncompressed blocks stores data extracted for queries. ClickHouse uses this cache to speed up responses to repeated small queries. This setting protects the cache from trashing by queries that read a large amount of data. The [uncompressed_cache_size](../../operations/server-configuration-parameters/settings.md/#server-settings-uncompressed_cache_size) server setting defines the size of the cache of uncompressed blocks.
Possible values:
@ -594,7 +594,7 @@ Default value: `1`.
Setting up query logging.
Queries sent to ClickHouse with this setup are logged according to the rules in the [query_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query-log) server configuration parameter.
Queries sent to ClickHouse with this setup are logged according to the rules in the [query_log](../../operations/server-configuration-parameters/settings.md/#server_configuration_parameters-query-log) server configuration parameter.
Example:
@ -639,7 +639,7 @@ log_queries_min_type='EXCEPTION_WHILE_PROCESSING'
Setting up query threads logging.
Query threads log into [system.query_thread_log](../../operations/system-tables/query_thread_log.md) table. This setting have effect only when [log_queries](#settings-log-queries) is true. Queries’ threads run by ClickHouse with this setup are logged according to the rules in the [query_thread_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query_thread_log) server configuration parameter.
Query threads log into [system.query_thread_log](../../operations/system-tables/query_thread_log.md) table. This setting have effect only when [log_queries](#settings-log-queries) is true. Queries’ threads run by ClickHouse with this setup are logged according to the rules in the [query_thread_log](../../operations/server-configuration-parameters/settings.md/#server_configuration_parameters-query_thread_log) server configuration parameter.
Possible values:
@ -658,7 +658,7 @@ log_query_threads=1
Setting up query views logging.
When a query run by ClickHouse with this setup on has associated views (materialized or live views), they are logged in the [query_views_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query_views_log) server configuration parameter.
When a query run by ClickHouse with this setup on has associated views (materialized or live views), they are logged in the [query_views_log](../../operations/server-configuration-parameters/settings.md/#server_configuration_parameters-query_views_log) server configuration parameter.
Example:
@ -884,7 +884,7 @@ Default value: `5`.
## max_replicated_fetches_network_bandwidth_for_server {#max_replicated_fetches_network_bandwidth_for_server}
Limits the maximum speed of data exchange over the network in bytes per second for [replicated](../../engines/table-engines/mergetree-family/replication.md) fetches for the server. Only has meaning at server startup. You can also limit the speed for a particular table with [max_replicated_fetches_network_bandwidth](../../operations/settings/merge-tree-settings.md#max_replicated_fetches_network_bandwidth) setting.
Limits the maximum speed of data exchange over the network in bytes per second for [replicated](../../engines/table-engines/mergetree-family/replication.md) fetches for the server. Only has meaning at server startup. You can also limit the speed for a particular table with [max_replicated_fetches_network_bandwidth](../../operations/settings/merge-tree-settings.md/#max_replicated_fetches_network_bandwidth) setting.
The setting isn't followed perfectly accurately.
@ -905,7 +905,7 @@ Could be used for throttling speed when replicating the data to add or replace n
## max_replicated_sends_network_bandwidth_for_server {#max_replicated_sends_network_bandwidth_for_server}
Limits the maximum speed of data exchange over the network in bytes per second for [replicated](../../engines/table-engines/mergetree-family/replication.md) sends for the server. Only has meaning at server startup. You can also limit the speed for a particular table with [max_replicated_sends_network_bandwidth](../../operations/settings/merge-tree-settings.md#max_replicated_sends_network_bandwidth) setting.
Limits the maximum speed of data exchange over the network in bytes per second for [replicated](../../engines/table-engines/mergetree-family/replication.md) sends for the server. Only has meaning at server startup. You can also limit the speed for a particular table with [max_replicated_sends_network_bandwidth](../../operations/settings/merge-tree-settings.md/#max_replicated_sends_network_bandwidth) setting.
The setting isn't followed perfectly accurately.
@ -955,7 +955,7 @@ For more information, see the section “Extreme values”.
## kafka_max_wait_ms {#kafka-max-wait-ms}
The wait time in milliseconds for reading messages from [Kafka](../../engines/table-engines/integrations/kafka.md#kafka) before retry.
The wait time in milliseconds for reading messages from [Kafka](../../engines/table-engines/integrations/kafka.md/#kafka) before retry.
Possible values:
@ -977,7 +977,7 @@ Default value: false.
## use_uncompressed_cache {#setting-use_uncompressed_cache}
Whether to use a cache of uncompressed blocks. Accepts 0 or 1. By default, 0 (disabled).
Using the uncompressed cache (only for tables in the MergeTree family) can significantly reduce latency and increase throughput when working with a large number of short queries. Enable this setting for users who send frequent short requests. Also pay attention to the [uncompressed_cache_size](../../operations/server-configuration-parameters/settings.md#server-settings-uncompressed_cache_size) configuration parameter (only set in the config file) – the size of uncompressed cache blocks. By default, it is 8 GiB. The uncompressed cache is filled in as needed and the least-used data is automatically deleted.
Using the uncompressed cache (only for tables in the MergeTree family) can significantly reduce latency and increase throughput when working with a large number of short queries. Enable this setting for users who send frequent short requests. Also pay attention to the [uncompressed_cache_size](../../operations/server-configuration-parameters/settings.md/#server-settings-uncompressed_cache_size) configuration parameter (only set in the config file) – the size of uncompressed cache blocks. By default, it is 8 GiB. The uncompressed cache is filled in as needed and the least-used data is automatically deleted.
For queries that read at least a somewhat large volume of data (one million rows or more), the uncompressed cache is disabled automatically to save space for truly small queries. This means that you can keep the ‘use_uncompressed_cache’ setting always set to 1.
@ -1124,7 +1124,7 @@ This setting is useful for replicated tables with a sampling key. A query may be
- The cluster latency distribution has a long tail, so that querying more servers increases the query overall latency.
:::warning
This setting will produce incorrect results when joins or subqueries are involved, and all tables don't meet certain requirements. See [Distributed Subqueries and max_parallel_replicas](../../sql-reference/operators/in.md#max_parallel_replica-subqueries) for more details.
This setting will produce incorrect results when joins or subqueries are involved, and all tables don't meet certain requirements. See [Distributed Subqueries and max_parallel_replicas](../../sql-reference/operators/in.md/#max_parallel_replica-subqueries) for more details.
:::
## compile_expressions {#compile-expressions}
@ -1261,7 +1261,7 @@ Possible values:
Default value: 1.
By default, blocks inserted into replicated tables by the `INSERT` statement are deduplicated (see [Data Replication](../../engines/table-engines/mergetree-family/replication.md)).
For the replicated tables by default the only 100 of the most recent blocks for each partition are deduplicated (see [replicated_deduplication_window](merge-tree-settings.md#replicated-deduplication-window), [replicated_deduplication_window_seconds](merge-tree-settings.md/#replicated-deduplication-window-seconds)).
For the replicated tables by default the only 100 of the most recent blocks for each partition are deduplicated (see [replicated_deduplication_window](merge-tree-settings.md/#replicated-deduplication-window), [replicated_deduplication_window_seconds](merge-tree-settings.md/#replicated-deduplication-window-seconds)).
For not replicated tables see [non_replicated_deduplication_window](merge-tree-settings.md/#non-replicated-deduplication-window).
## deduplicate_blocks_in_dependent_materialized_views {#settings-deduplicate-blocks-in-dependent-materialized-views}
@ -1296,7 +1296,7 @@ Default value: empty string (disabled)
`insert_deduplication_token` is used for deduplication _only_ when not empty.
For the replicated tables by default the only 100 of the most recent inserts for each partition are deduplicated (see [replicated_deduplication_window](merge-tree-settings.md#replicated-deduplication-window), [replicated_deduplication_window_seconds](merge-tree-settings.md/#replicated-deduplication-window-seconds)).
For the replicated tables by default the only 100 of the most recent inserts for each partition are deduplicated (see [replicated_deduplication_window](merge-tree-settings.md/#replicated-deduplication-window), [replicated_deduplication_window_seconds](merge-tree-settings.md/#replicated-deduplication-window-seconds)).
For not replicated tables see [non_replicated_deduplication_window](merge-tree-settings.md/#non-replicated-deduplication-window).
Example:
@ -1373,15 +1373,15 @@ Default value: 0.
## count_distinct_implementation {#settings-count_distinct_implementation}
Specifies which of the `uniq*` functions should be used to perform the [COUNT(DISTINCT …)](../../sql-reference/aggregate-functions/reference/count.md#agg_function-count) construction.
Specifies which of the `uniq*` functions should be used to perform the [COUNT(DISTINCT …)](../../sql-reference/aggregate-functions/reference/count.md/#agg_function-count) construction.
Possible values:
- [uniq](../../sql-reference/aggregate-functions/reference/uniq.md#agg_function-uniq)
- [uniqCombined](../../sql-reference/aggregate-functions/reference/uniqcombined.md#agg_function-uniqcombined)
- [uniqCombined64](../../sql-reference/aggregate-functions/reference/uniqcombined64.md#agg_function-uniqcombined64)
- [uniqHLL12](../../sql-reference/aggregate-functions/reference/uniqhll12.md#agg_function-uniqhll12)
- [uniqExact](../../sql-reference/aggregate-functions/reference/uniqexact.md#agg_function-uniqexact)
- [uniq](../../sql-reference/aggregate-functions/reference/uniq.md/#agg_function-uniq)
- [uniqCombined](../../sql-reference/aggregate-functions/reference/uniqcombined.md/#agg_function-uniqcombined)
- [uniqCombined64](../../sql-reference/aggregate-functions/reference/uniqcombined64.md/#agg_function-uniqcombined64)
- [uniqHLL12](../../sql-reference/aggregate-functions/reference/uniqhll12.md/#agg_function-uniqhll12)
- [uniqExact](../../sql-reference/aggregate-functions/reference/uniqexact.md/#agg_function-uniqexact)
Default value: `uniqExact`.
@ -1616,14 +1616,14 @@ Enables or disables optimization by transforming some functions to reading subco
These functions can be transformed:
- [length](../../sql-reference/functions/array-functions.md#array_functions-length) to read the [size0](../../sql-reference/data-types/array.md#array-size) subcolumn.
- [empty](../../sql-reference/functions/array-functions.md#function-empty) to read the [size0](../../sql-reference/data-types/array.md#array-size) subcolumn.
- [notEmpty](../../sql-reference/functions/array-functions.md#function-notempty) to read the [size0](../../sql-reference/data-types/array.md#array-size) subcolumn.
- [isNull](../../sql-reference/operators/index.md#operator-is-null) to read the [null](../../sql-reference/data-types/nullable.md#finding-null) subcolumn.
- [isNotNull](../../sql-reference/operators/index.md#is-not-null) to read the [null](../../sql-reference/data-types/nullable.md#finding-null) subcolumn.
- [count](../../sql-reference/aggregate-functions/reference/count.md) to read the [null](../../sql-reference/data-types/nullable.md#finding-null) subcolumn.
- [mapKeys](../../sql-reference/functions/tuple-map-functions.md#mapkeys) to read the [keys](../../sql-reference/data-types/map.md#map-subcolumns) subcolumn.
- [mapValues](../../sql-reference/functions/tuple-map-functions.md#mapvalues) to read the [values](../../sql-reference/data-types/map.md#map-subcolumns) subcolumn.
- [length](../../sql-reference/functions/array-functions.md/#array_functions-length) to read the [size0](../../sql-reference/data-types/array.md/#array-size) subcolumn.
- [empty](../../sql-reference/functions/array-functions.md/#function-empty) to read the [size0](../../sql-reference/data-types/array.md/#array-size) subcolumn.
- [notEmpty](../../sql-reference/functions/array-functions.md/#function-notempty) to read the [size0](../../sql-reference/data-types/array.md/#array-size) subcolumn.
- [isNull](../../sql-reference/operators/index.md/#operator-is-null) to read the [null](../../sql-reference/data-types/nullable.md/#finding-null) subcolumn.
- [isNotNull](../../sql-reference/operators/index.md/#is-not-null) to read the [null](../../sql-reference/data-types/nullable.md/#finding-null) subcolumn.
- [count](../../sql-reference/aggregate-functions/reference/count.md) to read the [null](../../sql-reference/data-types/nullable.md/#finding-null) subcolumn.
- [mapKeys](../../sql-reference/functions/tuple-map-functions.md/#mapkeys) to read the [keys](../../sql-reference/data-types/map.md/#map-subcolumns) subcolumn.
- [mapValues](../../sql-reference/functions/tuple-map-functions.md/#mapvalues) to read the [values](../../sql-reference/data-types/map.md/#map-subcolumns) subcolumn.
Possible values:
@ -1782,7 +1782,7 @@ Default value: 1000000000 nanoseconds (once a second).
See also:
- System table [trace_log](../../operations/system-tables/trace_log.md#system_tables-trace_log)
- System table [trace_log](../../operations/system-tables/trace_log.md/#system_tables-trace_log)
## query_profiler_cpu_time_period_ns {#query_profiler_cpu_time_period_ns}
@ -1805,7 +1805,7 @@ Default value: 1000000000 nanoseconds.
See also:
- System table [trace_log](../../operations/system-tables/trace_log.md#system_tables-trace_log)
- System table [trace_log](../../operations/system-tables/trace_log.md/#system_tables-trace_log)
## allow_introspection_functions {#settings-allow_introspection_functions}
@ -1821,11 +1821,11 @@ Default value: 0.
**See Also**
- [Sampling Query Profiler](../../operations/optimizing-performance/sampling-query-profiler.md)
- System table [trace_log](../../operations/system-tables/trace_log.md#system_tables-trace_log)
- System table [trace_log](../../operations/system-tables/trace_log.md/#system_tables-trace_log)
## input_format_parallel_parsing {#input-format-parallel-parsing}
Enables or disables order-preserving parallel parsing of data formats. Supported only for [TSV](../../interfaces/formats.md#tabseparated), [TKSV](../../interfaces/formats.md#tskv), [CSV](../../interfaces/formats.md#csv) and [JSONEachRow](../../interfaces/formats.md#jsoneachrow) formats.
Enables or disables order-preserving parallel parsing of data formats. Supported only for [TSV](../../interfaces/formats.md/#tabseparated), [TKSV](../../interfaces/formats.md/#tskv), [CSV](../../interfaces/formats.md/#csv) and [JSONEachRow](../../interfaces/formats.md/#jsoneachrow) formats.
Possible values:
@ -1836,7 +1836,7 @@ Default value: `1`.
## output_format_parallel_formatting {#output-format-parallel-formatting}
Enables or disables parallel formatting of data formats. Supported only for [TSV](../../interfaces/formats.md#tabseparated), [TKSV](../../interfaces/formats.md#tskv), [CSV](../../interfaces/formats.md#csv) and [JSONEachRow](../../interfaces/formats.md#jsoneachrow) formats.
Enables or disables parallel formatting of data formats. Supported only for [TSV](../../interfaces/formats.md/#tabseparated), [TKSV](../../interfaces/formats.md/#tskv), [CSV](../../interfaces/formats.md/#csv) and [JSONEachRow](../../interfaces/formats.md/#jsoneachrow) formats.
Possible values:
@ -1878,7 +1878,7 @@ Default value: 0.
## insert_distributed_sync {#insert_distributed_sync}
Enables or disables synchronous data insertion into a [Distributed](../../engines/table-engines/special/distributed.md#distributed) table.
Enables or disables synchronous data insertion into a [Distributed](../../engines/table-engines/special/distributed.md/#distributed) table.
By default, when inserting data into a `Distributed` table, the ClickHouse server sends data to cluster nodes in asynchronous mode. When `insert_distributed_sync=1`, the data is processed synchronously, and the `INSERT` operation succeeds only after all the data is saved on all shards (at least one replica for each shard if `internal_replication` is true).
@ -1891,12 +1891,12 @@ Default value: `0`.
**See Also**
- [Distributed Table Engine](../../engines/table-engines/special/distributed.md#distributed)
- [Managing Distributed Tables](../../sql-reference/statements/system.md#query-language-system-distributed)
- [Distributed Table Engine](../../engines/table-engines/special/distributed.md/#distributed)
- [Managing Distributed Tables](../../sql-reference/statements/system.md/#query-language-system-distributed)
## insert_shard_id {#insert_shard_id}
If not `0`, specifies the shard of [Distributed](../../engines/table-engines/special/distributed.md#distributed) table into which the data will be inserted synchronously.
If not `0`, specifies the shard of [Distributed](../../engines/table-engines/special/distributed.md/#distributed) table into which the data will be inserted synchronously.
If `insert_shard_id` value is incorrect, the server will throw an exception.
@ -1909,7 +1909,7 @@ SELECT uniq(shard_num) FROM system.clusters WHERE cluster = 'requested_cluster';
Possible values:
- 0 — Disabled.
- Any number from `1` to `shards_num` of corresponding [Distributed](../../engines/table-engines/special/distributed.md#distributed) table.
- Any number from `1` to `shards_num` of corresponding [Distributed](../../engines/table-engines/special/distributed.md/#distributed) table.
Default value: `0`.
@ -1969,7 +1969,7 @@ Default value: 16.
## background_move_pool_size {#background_move_pool_size}
Sets the number of threads performing background moves of data parts for [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-multiple-volumes)-engine tables. This setting is applied at the ClickHouse server start and can’t be changed in a user session.
Sets the number of threads performing background moves of data parts for [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-multiple-volumes)-engine tables. This setting is applied at the ClickHouse server start and can’t be changed in a user session.
Possible values:
@ -1979,7 +1979,7 @@ Default value: 8.
## background_schedule_pool_size {#background_schedule_pool_size}
Sets the number of threads performing background tasks for [replicated](../../engines/table-engines/mergetree-family/replication.md) tables, [Kafka](../../engines/table-engines/integrations/kafka.md) streaming, [DNS cache updates](../../operations/server-configuration-parameters/settings.md#server-settings-dns-cache-update-period). This setting is applied at ClickHouse server start and can’t be changed in a user session.
Sets the number of threads performing background tasks for [replicated](../../engines/table-engines/mergetree-family/replication.md) tables, [Kafka](../../engines/table-engines/integrations/kafka.md) streaming, [DNS cache updates](../../operations/server-configuration-parameters/settings.md/#server-settings-dns-cache-update-period). This setting is applied at ClickHouse server start and can’t be changed in a user session.
Possible values:
@ -2036,12 +2036,12 @@ Default value: 16.
**See Also**
- [Kafka](../../engines/table-engines/integrations/kafka.md#kafka) engine.
- [RabbitMQ](../../engines/table-engines/integrations/rabbitmq.md#rabbitmq-engine) engine.
- [Kafka](../../engines/table-engines/integrations/kafka.md/#kafka) engine.
- [RabbitMQ](../../engines/table-engines/integrations/rabbitmq.md/#rabbitmq-engine) engine.
## validate_polygons {#validate_polygons}
Enables or disables throwing an exception in the [pointInPolygon](../../sql-reference/functions/geo/index.md#pointinpolygon) function, if the polygon is self-intersecting or self-tangent.
Enables or disables throwing an exception in the [pointInPolygon](../../sql-reference/functions/geo/index.md/#pointinpolygon) function, if the polygon is self-intersecting or self-tangent.
Possible values:
@ -2052,7 +2052,7 @@ Default value: 1.
## transform_null_in {#transform_null_in}
Enables equality of [NULL](../../sql-reference/syntax.md#null-literal) values for [IN](../../sql-reference/operators/in.md) operator.
Enables equality of [NULL](../../sql-reference/syntax.md/#null-literal) values for [IN](../../sql-reference/operators/in.md) operator.
By default, `NULL` values can’t be compared because `NULL` means undefined value. Thus, comparison `expr = NULL` must always return `false`. With this setting `NULL = NULL` returns `true` for `IN` operator.
@ -2106,7 +2106,7 @@ Result:
**See Also**
- [NULL Processing in IN Operators](../../sql-reference/operators/in.md#in-null-processing)
- [NULL Processing in IN Operators](../../sql-reference/operators/in.md/#in-null-processing)
## low_cardinality_max_dictionary_size {#low_cardinality_max_dictionary_size}
@ -2133,7 +2133,7 @@ Default value: 0.
## low_cardinality_allow_in_native_format {#low_cardinality_allow_in_native_format}
Allows or restricts using the [LowCardinality](../../sql-reference/data-types/lowcardinality.md) data type with the [Native](../../interfaces/formats.md#native) format.
Allows or restricts using the [LowCardinality](../../sql-reference/data-types/lowcardinality.md) data type with the [Native](../../interfaces/formats.md/#native) format.
If usage of `LowCardinality` is restricted, ClickHouse server converts `LowCardinality`-columns to ordinary ones for `SELECT` queries, and convert ordinary columns to `LowCardinality`-columns for `INSERT` queries.
@ -2197,7 +2197,7 @@ Default value: 268435456.
## optimize_read_in_order {#optimize_read_in_order}
Enables [ORDER BY](../../sql-reference/statements/select/order-by.md#optimize_read_in_order) optimization in [SELECT](../../sql-reference/statements/select/index.md) queries for reading data from [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) tables.
Enables [ORDER BY](../../sql-reference/statements/select/order-by.md/#optimize_read_in_order) optimization in [SELECT](../../sql-reference/statements/select/index.md) queries for reading data from [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) tables.
Possible values:
@ -2208,7 +2208,7 @@ Default value: `1`.
**See Also**
- [ORDER BY Clause](../../sql-reference/statements/select/order-by.md#optimize_read_in_order)
- [ORDER BY Clause](../../sql-reference/statements/select/order-by.md/#optimize_read_in_order)
## optimize_aggregation_in_order {#optimize_aggregation_in_order}
@ -2223,11 +2223,11 @@ Default value: `0`.
**See Also**
- [GROUP BY optimization](../../sql-reference/statements/select/group-by.md#aggregation-in-order)
- [GROUP BY optimization](../../sql-reference/statements/select/group-by.md/#aggregation-in-order)
## mutations_sync {#mutations_sync}
Allows to execute `ALTER TABLE ... UPDATE|DELETE` queries ([mutations](../../sql-reference/statements/alter/index.md#mutations)) synchronously.
Allows to execute `ALTER TABLE ... UPDATE|DELETE` queries ([mutations](../../sql-reference/statements/alter/index.md/#mutations)) synchronously.
Possible values:
@ -2239,8 +2239,8 @@ Default value: `0`.
**See Also**
- [Synchronicity of ALTER Queries](../../sql-reference/statements/alter/index.md#synchronicity-of-alter-queries)
- [Mutations](../../sql-reference/statements/alter/index.md#mutations)
- [Synchronicity of ALTER Queries](../../sql-reference/statements/alter/index.md/#synchronicity-of-alter-queries)
- [Mutations](../../sql-reference/statements/alter/index.md/#mutations)
## ttl_only_drop_parts {#ttl_only_drop_parts}
@ -2261,8 +2261,8 @@ Default value: `0`.
**See Also**
- [CREATE TABLE query clauses and settings](../../engines/table-engines/mergetree-family/mergetree.md#mergetree-query-clauses) (`merge_with_ttl_timeout` setting)
- [Table TTL](../../engines/table-engines/mergetree-family/mergetree.md#mergetree-table-ttl)
- [CREATE TABLE query clauses and settings](../../engines/table-engines/mergetree-family/mergetree.md/#mergetree-query-clauses) (`merge_with_ttl_timeout` setting)
- [Table TTL](../../engines/table-engines/mergetree-family/mergetree.md/#mergetree-table-ttl)
## lock_acquire_timeout {#lock_acquire_timeout}
@ -2279,7 +2279,7 @@ Default value: `120` seconds.
## cast_keep_nullable {#cast_keep_nullable}
Enables or disables keeping of the `Nullable` data type in [CAST](../../sql-reference/functions/type-conversion-functions.md#type_conversion_function-cast) operations.
Enables or disables keeping of the `Nullable` data type in [CAST](../../sql-reference/functions/type-conversion-functions.md/#type_conversion_function-cast) operations.
When the setting is enabled and the argument of `CAST` function is `Nullable`, the result is also transformed to `Nullable` type. When the setting is disabled, the result always has the destination type exactly.
@ -2324,7 +2324,7 @@ Result:
**See Also**
- [CAST](../../sql-reference/functions/type-conversion-functions.md#type_conversion_function-cast) function
- [CAST](../../sql-reference/functions/type-conversion-functions.md/#type_conversion_function-cast) function
## system_events_show_zero_values {#system_events_show_zero_values}
@ -2369,7 +2369,7 @@ Result
## persistent {#persistent}
Disables persistency for the [Set](../../engines/table-engines/special/set.md#set) and [Join](../../engines/table-engines/special/join.md#join) table engines.
Disables persistency for the [Set](../../engines/table-engines/special/set.md/#set) and [Join](../../engines/table-engines/special/join.md/#join) table engines.
Reduces the I/O overhead. Suitable for scenarios that pursue performance and do not require persistence.
@ -2382,7 +2382,7 @@ Default value: `1`.
## allow_nullable_key {#allow-nullable-key}
Allows using of the [Nullable](../../sql-reference/data-types/nullable.md#data_type-nullable)-typed values in a sorting and a primary key for [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md#table_engines-mergetree) tables.
Allows using of the [Nullable](../../sql-reference/data-types/nullable.md/#data_type-nullable)-typed values in a sorting and a primary key for [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md/#table_engines-mergetree) tables.
Possible values:
@ -2401,7 +2401,7 @@ Do not enable this feature in version `<= 21.8`. It's not properly implemented a
## aggregate_functions_null_for_empty {#aggregate_functions_null_for_empty}
Enables or disables rewriting all aggregate functions in a query, adding [-OrNull](../../sql-reference/aggregate-functions/combinators.md#agg-functions-combinator-ornull) suffix to them. Enable it for SQL standard compatibility.
Enables or disables rewriting all aggregate functions in a query, adding [-OrNull](../../sql-reference/aggregate-functions/combinators.md/#agg-functions-combinator-ornull) suffix to them. Enable it for SQL standard compatibility.
It is implemented via query rewrite (similar to [count_distinct_implementation](#settings-count_distinct_implementation) setting) to get consistent results for distributed queries.
Possible values:
@ -2448,7 +2448,7 @@ See examples in [UNION](../../sql-reference/statements/select/union.md).
## data_type_default_nullable {#data_type_default_nullable}
Allows data types without explicit modifiers [NULL or NOT NULL](../../sql-reference/statements/create/table.md#null-modifiers) in column definition will be [Nullable](../../sql-reference/data-types/nullable.md#data_type-nullable).
Allows data types without explicit modifiers [NULL or NOT NULL](../../sql-reference/statements/create/table.md/#null-modifiers) in column definition will be [Nullable](../../sql-reference/data-types/nullable.md/#data_type-nullable).
Possible values:
@ -2478,7 +2478,7 @@ It can be useful when merges are CPU bounded not IO bounded (performing heavy da
## max_final_threads {#max-final-threads}
Sets the maximum number of parallel threads for the `SELECT` query data read phase with the [FINAL](../../sql-reference/statements/select/from.md#select-from-final) modifier.
Sets the maximum number of parallel threads for the `SELECT` query data read phase with the [FINAL](../../sql-reference/statements/select/from.md/#select-from-final) modifier.
Possible values:
@ -2551,7 +2551,7 @@ Result:
└─────────────┘
```
Note that this setting influences [Materialized view](../../sql-reference/statements/create/view.md#materialized) and [MaterializedMySQL](../../engines/database-engines/materialized-mysql.md) behaviour.
Note that this setting influences [Materialized view](../../sql-reference/statements/create/view.md/#materialized) and [MaterializedMySQL](../../engines/database-engines/materialized-mysql.md) behaviour.
## engine_file_empty_if_not_exists {#engine-file-empty_if-not-exists}
@ -2608,7 +2608,7 @@ Default value: `0`.
## allow_experimental_live_view {#allow-experimental-live-view}
Allows creation of experimental [live views](../../sql-reference/statements/create/view.md#live-view).
Allows creation of experimental [live views](../../sql-reference/statements/create/view.md/#live-view).
Possible values:
@ -2619,19 +2619,19 @@ Default value: `0`.
## live_view_heartbeat_interval {#live-view-heartbeat-interval}
Sets the heartbeat interval in seconds to indicate [live view](../../sql-reference/statements/create/view.md#live-view) is alive .
Sets the heartbeat interval in seconds to indicate [live view](../../sql-reference/statements/create/view.md/#live-view) is alive .
Default value: `15`.
## max_live_view_insert_blocks_before_refresh {#max-live-view-insert-blocks-before-refresh}
Sets the maximum number of inserted blocks after which mergeable blocks are dropped and query for [live view](../../sql-reference/statements/create/view.md#live-view) is re-executed.
Sets the maximum number of inserted blocks after which mergeable blocks are dropped and query for [live view](../../sql-reference/statements/create/view.md/#live-view) is re-executed.
Default value: `64`.
## periodic_live_view_refresh {#periodic-live-view-refresh}
Sets the interval in seconds after which periodically refreshed [live view](../../sql-reference/statements/create/view.md#live-view) is forced to refresh.
Sets the interval in seconds after which periodically refreshed [live view](../../sql-reference/statements/create/view.md/#live-view) is forced to refresh.
Default value: `60`.
@ -2670,7 +2670,7 @@ Default value: 180.
## check_query_single_value_result {#check_query_single_value_result}
Defines the level of detail for the [CHECK TABLE](../../sql-reference/statements/check-table.md#checking-mergetree-tables) query result for `MergeTree` family engines .
Defines the level of detail for the [CHECK TABLE](../../sql-reference/statements/check-table.md/#checking-mergetree-tables) query result for `MergeTree` family engines .
Possible values:
@ -2681,7 +2681,7 @@ Default value: `0`.
## prefer_column_name_to_alias {#prefer-column-name-to-alias}
Enables or disables using the original column names instead of aliases in query expressions and clauses. It especially matters when alias is the same as the column name, see [Expression Aliases](../../sql-reference/syntax.md#notes-on-usage). Enable this setting to make aliases syntax rules in ClickHouse more compatible with most other database engines.
Enables or disables using the original column names instead of aliases in query expressions and clauses. It especially matters when alias is the same as the column name, see [Expression Aliases](../../sql-reference/syntax.md/#notes-on-usage). Enable this setting to make aliases syntax rules in ClickHouse more compatible with most other database engines.
Possible values:
@ -2725,7 +2725,7 @@ Result:
## limit {#limit}
Sets the maximum number of rows to get from the query result. It adjusts the value set by the [LIMIT](../../sql-reference/statements/select/limit.md#limit-clause) clause, so that the limit, specified in the query, cannot exceed the limit, set by this setting.
Sets the maximum number of rows to get from the query result. It adjusts the value set by the [LIMIT](../../sql-reference/statements/select/limit.md/#limit-clause) clause, so that the limit, specified in the query, cannot exceed the limit, set by this setting.
Possible values:
@ -2736,7 +2736,7 @@ Default value: `0`.
## offset {#offset}
Sets the number of rows to skip before starting to return rows from the query. It adjusts the offset set by the [OFFSET](../../sql-reference/statements/select/offset.md#offset-fetch) clause, so that these two values are summarized.
Sets the number of rows to skip before starting to return rows from the query. It adjusts the offset set by the [OFFSET](../../sql-reference/statements/select/offset.md/#offset-fetch) clause, so that these two values are summarized.
Possible values:
@ -2773,7 +2773,7 @@ Result:
## optimize_syntax_fuse_functions {#optimize_syntax_fuse_functions}
Enables to fuse aggregate functions with identical argument. It rewrites query contains at least two aggregate functions from [sum](../../sql-reference/aggregate-functions/reference/sum.md#agg_function-sum), [count](../../sql-reference/aggregate-functions/reference/count.md#agg_function-count) or [avg](../../sql-reference/aggregate-functions/reference/avg.md#agg_function-avg) with identical argument to [sumCount](../../sql-reference/aggregate-functions/reference/sumcount.md#agg_function-sumCount).
Enables to fuse aggregate functions with identical argument. It rewrites query contains at least two aggregate functions from [sum](../../sql-reference/aggregate-functions/reference/sum.md/#agg_function-sum), [count](../../sql-reference/aggregate-functions/reference/count.md/#agg_function-count) or [avg](../../sql-reference/aggregate-functions/reference/avg.md/#agg_function-avg) with identical argument to [sumCount](../../sql-reference/aggregate-functions/reference/sumcount.md/#agg_function-sumCount).
Possible values:
@ -2932,7 +2932,7 @@ If the setting is set to `0`, the table function does not make Nullable columns
## allow_experimental_projection_optimization {#allow-experimental-projection-optimization}
Enables or disables [projection](../../engines/table-engines/mergetree-family/mergetree.md#projections) optimization when processing `SELECT` queries.
Enables or disables [projection](../../engines/table-engines/mergetree-family/mergetree.md/#projections) optimization when processing `SELECT` queries.
Possible values:
@ -2943,7 +2943,7 @@ Default value: `1`.
## force_optimize_projection {#force-optimize-projection}
Enables or disables the obligatory use of [projections](../../engines/table-engines/mergetree-family/mergetree.md#projections) in `SELECT` queries, when projection optimization is enabled (see [allow_experimental_projection_optimization](#allow-experimental-projection-optimization) setting).
Enables or disables the obligatory use of [projections](../../engines/table-engines/mergetree-family/mergetree.md/#projections) in `SELECT` queries, when projection optimization is enabled (see [allow_experimental_projection_optimization](#allow-experimental-projection-optimization) setting).
Possible values:
@ -2978,7 +2978,7 @@ Default value: `120` seconds.
## regexp_max_matches_per_row {#regexp-max-matches-per-row}
Sets the maximum number of matches for a single regular expression per row. Use it to protect against memory overload when using greedy regular expression in the [extractAllGroupsHorizontal](../../sql-reference/functions/string-search-functions.md#extractallgroups-horizontal) function.
Sets the maximum number of matches for a single regular expression per row. Use it to protect against memory overload when using greedy regular expression in the [extractAllGroupsHorizontal](../../sql-reference/functions/string-search-functions.md/#extractallgroups-horizontal) function.
Possible values:
@ -3010,7 +3010,7 @@ Default value: `1`.
## short_circuit_function_evaluation {#short-circuit-function-evaluation}
Allows calculating the [if](../../sql-reference/functions/conditional-functions.md#if), [multiIf](../../sql-reference/functions/conditional-functions.md#multiif), [and](../../sql-reference/functions/logical-functions.md#logical-and-function), and [or](../../sql-reference/functions/logical-functions.md#logical-or-function) functions according to a [short scheme](https://en.wikipedia.org/wiki/Short-circuit_evaluation). This helps optimize the execution of complex expressions in these functions and prevent possible exceptions (such as division by zero when it is not expected).
Allows calculating the [if](../../sql-reference/functions/conditional-functions.md/#if), [multiIf](../../sql-reference/functions/conditional-functions.md/#multiif), [and](../../sql-reference/functions/logical-functions.md/#logical-and-function), and [or](../../sql-reference/functions/logical-functions.md/#logical-or-function) functions according to a [short scheme](https://en.wikipedia.org/wiki/Short-circuit_evaluation). This helps optimize the execution of complex expressions in these functions and prevent possible exceptions (such as division by zero when it is not expected).
Possible values:
@ -3022,7 +3022,7 @@ Default value: `enable`.
## max_hyperscan_regexp_length {#max-hyperscan-regexp-length}
Defines the maximum length for each regular expression in the [hyperscan multi-match functions](../../sql-reference/functions/string-search-functions.md#multimatchanyhaystack-pattern1-pattern2-patternn).
Defines the maximum length for each regular expression in the [hyperscan multi-match functions](../../sql-reference/functions/string-search-functions.md/#multimatchanyhaystack-pattern1-pattern2-patternn).
Possible values:
@ -3065,7 +3065,7 @@ Exception: Regexp length too large.
## max_hyperscan_regexp_total_length {#max-hyperscan-regexp-total-length}
Sets the maximum length total of all regular expressions in each [hyperscan multi-match function](../../sql-reference/functions/string-search-functions.md#multimatchanyhaystack-pattern1-pattern2-patternn).
Sets the maximum length total of all regular expressions in each [hyperscan multi-match function](../../sql-reference/functions/string-search-functions.md/#multimatchanyhaystack-pattern1-pattern2-patternn).
Possible values:
@ -3142,8 +3142,8 @@ Result:
## enable_extended_results_for_datetime_functions {#enable-extended-results-for-datetime-functions}
Enables or disables returning results of type:
- `Date32` with extended range (compared to type `Date`) for functions [toStartOfYear](../../sql-reference/functions/date-time-functions.md#tostartofyear), [toStartOfISOYear](../../sql-reference/functions/date-time-functions.md#tostartofisoyear), [toStartOfQuarter](../../sql-reference/functions/date-time-functions.md#tostartofquarter), [toStartOfMonth](../../sql-reference/functions/date-time-functions.md#tostartofmonth), [toStartOfWeek](../../sql-reference/functions/date-time-functions.md#tostartofweek), [toMonday](../../sql-reference/functions/date-time-functions.md#tomonday) and [toLastDayOfMonth](../../sql-reference/functions/date-time-functions.md#tolastdayofmonth).
- `DateTime64` with extended range (compared to type `DateTime`) for functions [toStartOfDay](../../sql-reference/functions/date-time-functions.md#tostartofday), [toStartOfHour](../../sql-reference/functions/date-time-functions.md#tostartofhour), [toStartOfMinute](../../sql-reference/functions/date-time-functions.md#tostartofminute), [toStartOfFiveMinutes](../../sql-reference/functions/date-time-functions.md#tostartoffiveminutes), [toStartOfTenMinutes](../../sql-reference/functions/date-time-functions.md#tostartoftenminutes), [toStartOfFifteenMinutes](../../sql-reference/functions/date-time-functions.md#tostartoffifteenminutes) and [timeSlot](../../sql-reference/functions/date-time-functions.md#timeslot).
- `Date32` with extended range (compared to type `Date`) for functions [toStartOfYear](../../sql-reference/functions/date-time-functions.md/#tostartofyear), [toStartOfISOYear](../../sql-reference/functions/date-time-functions.md/#tostartofisoyear), [toStartOfQuarter](../../sql-reference/functions/date-time-functions.md/#tostartofquarter), [toStartOfMonth](../../sql-reference/functions/date-time-functions.md/#tostartofmonth), [toStartOfWeek](../../sql-reference/functions/date-time-functions.md/#tostartofweek), [toMonday](../../sql-reference/functions/date-time-functions.md/#tomonday) and [toLastDayOfMonth](../../sql-reference/functions/date-time-functions.md/#tolastdayofmonth).
- `DateTime64` with extended range (compared to type `DateTime`) for functions [toStartOfDay](../../sql-reference/functions/date-time-functions.md/#tostartofday), [toStartOfHour](../../sql-reference/functions/date-time-functions.md/#tostartofhour), [toStartOfMinute](../../sql-reference/functions/date-time-functions.md/#tostartofminute), [toStartOfFiveMinutes](../../sql-reference/functions/date-time-functions.md/#tostartoffiveminutes), [toStartOfTenMinutes](../../sql-reference/functions/date-time-functions.md/#tostartoftenminutes), [toStartOfFifteenMinutes](../../sql-reference/functions/date-time-functions.md/#tostartoffifteenminutes) and [timeSlot](../../sql-reference/functions/date-time-functions.md/#timeslot).
Possible values:
@ -3167,7 +3167,7 @@ Default value: `1`.
## optimize_move_to_prewhere_if_final {#optimize_move_to_prewhere_if_final}
Enables or disables automatic [PREWHERE](../../sql-reference/statements/select/prewhere.md) optimization in [SELECT](../../sql-reference/statements/select/index.md) queries with [FINAL](../../sql-reference/statements/select/from.md#select-from-final) modifier.
Enables or disables automatic [PREWHERE](../../sql-reference/statements/select/prewhere.md) optimization in [SELECT](../../sql-reference/statements/select/index.md) queries with [FINAL](../../sql-reference/statements/select/from.md/#select-from-final) modifier.
Works only for [*MergeTree](../../engines/table-engines/mergetree-family/index.md) tables.
@ -3184,7 +3184,7 @@ Default value: `0`.
## describe_include_subcolumns {#describe_include_subcolumns}
Enables describing subcolumns for a [DESCRIBE](../../sql-reference/statements/describe-table.md) query. For example, members of a [Tuple](../../sql-reference/data-types/tuple.md) or subcolumns of a [Map](../../sql-reference/data-types/map.md#map-subcolumns), [Nullable](../../sql-reference/data-types/nullable.md#finding-null) or an [Array](../../sql-reference/data-types/array.md#array-size) data type.
Enables describing subcolumns for a [DESCRIBE](../../sql-reference/statements/describe-table.md) query. For example, members of a [Tuple](../../sql-reference/data-types/tuple.md) or subcolumns of a [Map](../../sql-reference/data-types/map.md/#map-subcolumns), [Nullable](../../sql-reference/data-types/nullable.md/#finding-null) or an [Array](../../sql-reference/data-types/array.md/#array-size) data type.
Possible values:
@ -3283,7 +3283,7 @@ Default value: `0`.
## alter_partition_verbose_result {#alter-partition-verbose-result}
Enables or disables the display of information about the parts to which the manipulation operations with partitions and parts have been successfully applied.
Applicable to [ATTACH PARTITION|PART](../../sql-reference/statements/alter/partition.md#alter_attach-partition) and to [FREEZE PARTITION](../../sql-reference/statements/alter/partition.md#alter_freeze-partition).
Applicable to [ATTACH PARTITION|PART](../../sql-reference/statements/alter/partition.md/#alter_attach-partition) and to [FREEZE PARTITION](../../sql-reference/statements/alter/partition.md/#alter_freeze-partition).
Possible values:
@ -3399,6 +3399,17 @@ Use schema from cache for URL with last modification time validation (for urls w
Default value: `true`.
## use_structure_from_insertion_table_in_table_functions {use_structure_from_insertion_table_in_table_functions}
Use structure from insertion table instead of schema inference from data.
Possible values:
- 0 - disabled
- 1 - enabled
- 2 - auto
Default value: 2.
## compatibility {#compatibility}
This setting changes other settings according to provided ClickHouse version.
@ -3418,11 +3429,11 @@ When writing data, ClickHouse throws an exception if input data contain columns
Supported formats:
- [JSONEachRow](../../interfaces/formats.md#jsoneachrow)
- [TSKV](../../interfaces/formats.md#tskv)
- [JSONEachRow](../../interfaces/formats.md/#jsoneachrow)
- [TSKV](../../interfaces/formats.md/#tskv)
- All formats with suffixes WithNames/WithNamesAndTypes
- [JSONColumns](../../interfaces/formats.md#jsoncolumns)
- [MySQLDump](../../interfaces/formats.md#mysqldump)
- [JSONColumns](../../interfaces/formats.md/#jsoncolumns)
- [MySQLDump](../../interfaces/formats.md/#mysqldump)
Possible values:
@ -3439,18 +3450,18 @@ To improve insert performance, we recommend disabling this check if you are sure
Supported formats:
- [CSVWithNames](../../interfaces/formats.md#csvwithnames)
- [CSVWithNamesAndTypes](../../interfaces/formats.md#csvwithnamesandtypes)
- [TabSeparatedWithNames](../../interfaces/formats.md#tabseparatedwithnames)
- [TabSeparatedWithNamesAndTypes](../../interfaces/formats.md#tabseparatedwithnamesandtypes)
- [JSONCompactEachRowWithNames](../../interfaces/formats.md#jsoncompacteachrowwithnames)
- [JSONCompactEachRowWithNamesAndTypes](../../interfaces/formats.md#jsoncompacteachrowwithnamesandtypes)
- [JSONCompactStringsEachRowWithNames](../../interfaces/formats.md#jsoncompactstringseachrowwithnames)
- [JSONCompactStringsEachRowWithNamesAndTypes](../../interfaces/formats.md#jsoncompactstringseachrowwithnamesandtypes)
- [RowBinaryWithNames](../../interfaces/formats.md#rowbinarywithnames)
- [RowBinaryWithNamesAndTypes](../../interfaces/formats.md#rowbinarywithnamesandtypes)
- [CustomSeparatedWithNames](../../interfaces/formats.md#customseparatedwithnames)
- [CustomSeparatedWithNamesAndTypes](../../interfaces/formats.md#customseparatedwithnamesandtypes)
- [CSVWithNames](../../interfaces/formats.md/#csvwithnames)
- [CSVWithNamesAndTypes](../../interfaces/formats.md/#csvwithnamesandtypes)
- [TabSeparatedWithNames](../../interfaces/formats.md/#tabseparatedwithnames)
- [TabSeparatedWithNamesAndTypes](../../interfaces/formats.md/#tabseparatedwithnamesandtypes)
- [JSONCompactEachRowWithNames](../../interfaces/formats.md/#jsoncompacteachrowwithnames)
- [JSONCompactEachRowWithNamesAndTypes](../../interfaces/formats.md/#jsoncompacteachrowwithnamesandtypes)
- [JSONCompactStringsEachRowWithNames](../../interfaces/formats.md/#jsoncompactstringseachrowwithnames)
- [JSONCompactStringsEachRowWithNamesAndTypes](../../interfaces/formats.md/#jsoncompactstringseachrowwithnamesandtypes)
- [RowBinaryWithNames](../../interfaces/formats.md/#rowbinarywithnames)
- [RowBinaryWithNamesAndTypes](../../interfaces/formats.md/#rowbinarywithnamesandtypes)
- [CustomSeparatedWithNames](../../interfaces/formats.md/#customseparatedwithnames)
- [CustomSeparatedWithNamesAndTypes](../../interfaces/formats.md/#customseparatedwithnamesandtypes)
Possible values:
@ -3465,12 +3476,12 @@ Controls whether format parser should check if data types from the input data ma
Supported formats:
- [CSVWithNamesAndTypes](../../interfaces/formats.md#csvwithnamesandtypes)
- [TabSeparatedWithNamesAndTypes](../../interfaces/formats.md#tabseparatedwithnamesandtypes)
- [JSONCompactEachRowWithNamesAndTypes](../../interfaces/formats.md#jsoncompacteachrowwithnamesandtypes)
- [JSONCompactStringsEachRowWithNamesAndTypes](../../interfaces/formats.md#jsoncompactstringseachrowwithnamesandtypes)
- [RowBinaryWithNamesAndTypes](../../interfaces/formats.md#rowbinarywithnamesandtypes-rowbinarywithnamesandtypes)
- [CustomSeparatedWithNamesAndTypes](../../interfaces/formats.md#customseparatedwithnamesandtypes)
- [CSVWithNamesAndTypes](../../interfaces/formats.md/#csvwithnamesandtypes)
- [TabSeparatedWithNamesAndTypes](../../interfaces/formats.md/#tabseparatedwithnamesandtypes)
- [JSONCompactEachRowWithNamesAndTypes](../../interfaces/formats.md/#jsoncompacteachrowwithnamesandtypes)
- [JSONCompactStringsEachRowWithNamesAndTypes](../../interfaces/formats.md/#jsoncompactstringseachrowwithnamesandtypes)
- [RowBinaryWithNamesAndTypes](../../interfaces/formats.md/#rowbinarywithnamesandtypes-rowbinarywithnamesandtypes)
- [CustomSeparatedWithNamesAndTypes](../../interfaces/formats.md/#customseparatedwithnamesandtypes)
Possible values:
@ -3481,7 +3492,7 @@ Default value: 1.
## input_format_defaults_for_omitted_fields {#input_format_defaults_for_omitted_fields}
When performing `INSERT` queries, replace omitted input column values with default values of the respective columns. This option only applies to [JSONEachRow](../../interfaces/formats.md#jsoneachrow), [CSV](../../interfaces/formats.md#csv), [TabSeparated](../../interfaces/formats.md#tabseparated) formats and formats with `WithNames`/`WithNamesAndTypes` suffixes.
When performing `INSERT` queries, replace omitted input column values with default values of the respective columns. This option only applies to [JSONEachRow](../../interfaces/formats.md/#jsoneachrow), [CSV](../../interfaces/formats.md/#csv), [TabSeparated](../../interfaces/formats.md/#tabseparated) formats and formats with `WithNames`/`WithNamesAndTypes` suffixes.
:::note
When this option is enabled, extended table metadata are sent from server to client. It consumes additional computing resources on the server and can reduce performance.
@ -3496,7 +3507,7 @@ Default value: 1.
## input_format_null_as_default {#input_format_null_as_default}
Enables or disables the initialization of [NULL](../../sql-reference/syntax.md#null-literal) fields with [default values](../../sql-reference/statements/create/table.md#create-default-values), if data type of these fields is not [nullable](../../sql-reference/data-types/nullable.md#data_type-nullable).
Enables or disables the initialization of [NULL](../../sql-reference/syntax.md/#null-literal) fields with [default values](../../sql-reference/statements/create/table.md/#create-default-values), if data type of these fields is not [nullable](../../sql-reference/data-types/nullable.md/#data_type-nullable).
If column type is not nullable and this setting is disabled, then inserting `NULL` causes an exception. If column type is nullable, then `NULL` values are inserted as is, regardless of this setting.
This setting is applicable to [INSERT ... VALUES](../../sql-reference/statements/insert-into.md) queries for text input formats.
@ -3663,7 +3674,7 @@ Enabled by default
## insert_distributed_one_random_shard {#insert_distributed_one_random_shard}
Enables or disables random shard insertion into a [Distributed](../../engines/table-engines/special/distributed.md#distributed) table when there is no distributed key.
Enables or disables random shard insertion into a [Distributed](../../engines/table-engines/special/distributed.md/#distributed) table when there is no distributed key.
By default, when inserting data into a `Distributed` table with more than one shard, the ClickHouse server will reject any insertion request if there is no distributed key. When `insert_distributed_one_random_shard = 1`, insertions are allowed and data is forwarded randomly among all shards.
@ -3682,7 +3693,7 @@ Enables or disables the insertion of JSON data with nested objects.
Supported formats:
- [JSONEachRow](../../interfaces/formats.md#jsoneachrow)
- [JSONEachRow](../../interfaces/formats.md/#jsoneachrow)
Possible values:
@ -3693,7 +3704,7 @@ Default value: 0.
See also:
- [Usage of Nested Structures](../../interfaces/formats.md#jsoneachrow-nested) with the `JSONEachRow` format.
- [Usage of Nested Structures](../../interfaces/formats.md/#jsoneachrow-nested) with the `JSONEachRow` format.
### input_format_json_read_bools_as_numbers {#input_format_json_read_bools_as_numbers}
@ -3716,7 +3727,7 @@ Enabled by default.
### output_format_json_quote_64bit_integers {#output_format_json_quote_64bit_integers}
Controls quoting of 64-bit or bigger [integers](../../sql-reference/data-types/int-uint.md) (like `UInt64` or `Int128`) when they are output in a [JSON](../../interfaces/formats.md#json) format.
Controls quoting of 64-bit or bigger [integers](../../sql-reference/data-types/int-uint.md) (like `UInt64` or `Int128`) when they are output in a [JSON](../../interfaces/formats.md/#json) format.
Such integers are enclosed in quotes by default. This behavior is compatible with most JavaScript implementations.
Possible values:
@ -3734,7 +3745,7 @@ Disabled by default.
### output_format_json_quote_denormals {#output_format_json_quote_denormals}
Enables `+nan`, `-nan`, `+inf`, `-inf` outputs in [JSON](../../interfaces/formats.md#json) output format.
Enables `+nan`, `-nan`, `+inf`, `-inf` outputs in [JSON](../../interfaces/formats.md/#json) output format.
Possible values:
@ -3851,7 +3862,7 @@ Disabled by default.
### output_format_json_array_of_rows {#output_format_json_array_of_rows}
Enables the ability to output all rows as a JSON array in the [JSONEachRow](../../interfaces/formats.md#jsoneachrow) format.
Enables the ability to output all rows as a JSON array in the [JSONEachRow](../../interfaces/formats.md/#jsoneachrow) format.
Possible values:
@ -3904,7 +3915,7 @@ Disabled by default.
### format_json_object_each_row_column_for_object_name {#format_json_object_each_row_column_for_object_name}
The name of column that will be used for storing/writing object names in [JSONObjectEachRow](../../interfaces/formats.md#jsonobjecteachrow) format.
The name of column that will be used for storing/writing object names in [JSONObjectEachRow](../../interfaces/formats.md/#jsonobjecteachrow) format.
Column type should be String. If value is empty, default names `row_{i}`will be used for object names.
Default value: ''.
@ -4005,7 +4016,7 @@ Disabled by default.
### format_tsv_null_representation {#format_tsv_null_representation}
Defines the representation of `NULL` for [TSV](../../interfaces/formats.md#tabseparated) output and input formats. User can set any string as a value, for example, `My NULL`.
Defines the representation of `NULL` for [TSV](../../interfaces/formats.md/#tabseparated) output and input formats. User can set any string as a value, for example, `My NULL`.
Default value: `\N`.
@ -4159,7 +4170,7 @@ Default value: `0`.
### format_csv_null_representation {#format_csv_null_representation}
Defines the representation of `NULL` for [CSV](../../interfaces/formats.md#csv) output and input formats. User can set any string as a value, for example, `My NULL`.
Defines the representation of `NULL` for [CSV](../../interfaces/formats.md/#csv) output and input formats. User can set any string as a value, for example, `My NULL`.
Default value: `\N`.
@ -4198,7 +4209,7 @@ My NULL
### input_format_values_interpret_expressions {#input_format_values_interpret_expressions}
Enables or disables the full SQL parser if the fast stream parser can’t parse the data. This setting is used only for the [Values](../../interfaces/formats.md#data-format-values) format at the data insertion. For more information about syntax parsing, see the [Syntax](../../sql-reference/syntax.md) section.
Enables or disables the full SQL parser if the fast stream parser can’t parse the data. This setting is used only for the [Values](../../interfaces/formats.md/#data-format-values) format at the data insertion. For more information about syntax parsing, see the [Syntax](../../sql-reference/syntax.md) section.
Possible values:
@ -4248,7 +4259,7 @@ Ok.
### input_format_values_deduce_templates_of_expressions {#input_format_values_deduce_templates_of_expressions}
Enables or disables template deduction for SQL expressions in [Values](../../interfaces/formats.md#data-format-values) format. It allows parsing and interpreting expressions in `Values` much faster if expressions in consecutive rows have the same structure. ClickHouse tries to deduce the template of an expression, parse the following rows using this template and evaluate the expression on a batch of successfully parsed rows.
Enables or disables template deduction for SQL expressions in [Values](../../interfaces/formats.md/#data-format-values) format. It allows parsing and interpreting expressions in `Values` much faster if expressions in consecutive rows have the same structure. ClickHouse tries to deduce the template of an expression, parse the following rows using this template and evaluate the expression on a batch of successfully parsed rows.
Possible values:
@ -4293,7 +4304,7 @@ Default value: 1.
### input_format_arrow_import_nested {#input_format_arrow_import_nested}
Enables or disables the ability to insert the data into [Nested](../../sql-reference/data-types/nested-data-structures/nested.md) columns as an array of structs in [Arrow](../../interfaces/formats.md#data_types-matching-arrow) input format.
Enables or disables the ability to insert the data into [Nested](../../sql-reference/data-types/nested-data-structures/nested.md) columns as an array of structs in [Arrow](../../interfaces/formats.md/#data_types-matching-arrow) input format.
Possible values:
@ -4322,7 +4333,7 @@ Disabled by default.
### output_format_arrow_low_cardinality_as_dictionary {#output_format_arrow_low_cardinality_as_dictionary}
Allows to convert the [LowCardinality](../../sql-reference/data-types/lowcardinality.md) type to the `DICTIONARY` type of the [Arrow](../../interfaces/formats.md#data-format-arrow) format for `SELECT` queries.
Allows to convert the [LowCardinality](../../sql-reference/data-types/lowcardinality.md) type to the `DICTIONARY` type of the [Arrow](../../interfaces/formats.md/#data-format-arrow) format for `SELECT` queries.
Possible values:
@ -4341,7 +4352,7 @@ Disabled by default.
### input_format_orc_import_nested {#input_format_orc_import_nested}
Enables or disables the ability to insert the data into [Nested](../../sql-reference/data-types/nested-data-structures/nested.md) columns as an array of structs in [ORC](../../interfaces/formats.md#data-format-orc) input format.
Enables or disables the ability to insert the data into [Nested](../../sql-reference/data-types/nested-data-structures/nested.md) columns as an array of structs in [ORC](../../interfaces/formats.md/#data-format-orc) input format.
Possible values:
@ -4384,7 +4395,7 @@ Disabled by default.
## input_format_parquet_import_nested {#input_format_parquet_import_nested}
Enables or disables the ability to insert the data into [Nested](../../sql-reference/data-types/nested-data-structures/nested.md) columns as an array of structs in [Parquet](../../interfaces/formats.md#data-format-parquet) input format.
Enables or disables the ability to insert the data into [Nested](../../sql-reference/data-types/nested-data-structures/nested.md) columns as an array of structs in [Parquet](../../interfaces/formats.md/#data-format-parquet) input format.
Possible values:
@ -4481,7 +4492,7 @@ Disabled by default.
### input_format_avro_allow_missing_fields {#input_format_avro_allow_missing_fields}
Enables using fields that are not specified in [Avro](../../interfaces/formats.md#data-format-avro) or [AvroConfluent](../../interfaces/formats.md#data-format-avro-confluent) format schema. When a field is not found in the schema, ClickHouse uses the default value instead of throwing an exception.
Enables using fields that are not specified in [Avro](../../interfaces/formats.md/#data-format-avro) or [AvroConfluent](../../interfaces/formats.md/#data-format-avro-confluent) format schema. When a field is not found in the schema, ClickHouse uses the default value instead of throwing an exception.
Possible values:
@ -4492,7 +4503,7 @@ Default value: 0.
### format_avro_schema_registry_url {#format_avro_schema_registry_url}
Sets [Confluent Schema Registry](https://docs.confluent.io/current/schema-registry/index.html) URL to use with [AvroConfluent](../../interfaces/formats.md#data-format-avro-confluent) format.
Sets [Confluent Schema Registry](https://docs.confluent.io/current/schema-registry/index.html) URL to use with [AvroConfluent](../../interfaces/formats.md/#data-format-avro-confluent) format.
Default value: `Empty`.
@ -4549,7 +4560,7 @@ Default value: `250`.
### output_format_pretty_max_value_width {#output_format_pretty_max_value_width}
Limits the width of value displayed in [Pretty](../../interfaces/formats.md#pretty) formats. If the value width exceeds the limit, the value is cut.
Limits the width of value displayed in [Pretty](../../interfaces/formats.md/#pretty) formats. If the value width exceeds the limit, the value is cut.
Possible values:
@ -4625,7 +4636,7 @@ SELECT * FROM a;
### output_format_pretty_row_numbers {#output_format_pretty_row_numbers}
Adds row numbers to output in the [Pretty](../../interfaces/formats.md#pretty) format.
Adds row numbers to output in the [Pretty](../../interfaces/formats.md/#pretty) format.
Possible values:
@ -4670,52 +4681,52 @@ Delimiter between rows (for Template format).
### format_custom_escaping_rule {#format_custom_escaping_rule}
Sets the field escaping rule for [CustomSeparated](../../interfaces/formats.md#format-customseparated) data format.
Sets the field escaping rule for [CustomSeparated](../../interfaces/formats.md/#format-customseparated) data format.
Possible values:
- `'Escaped'` — Similarly to [TSV](../../interfaces/formats.md#tabseparated).
- `'Quoted'` — Similarly to [Values](../../interfaces/formats.md#data-format-values).
- `'CSV'` — Similarly to [CSV](../../interfaces/formats.md#csv).
- `'JSON'` — Similarly to [JSONEachRow](../../interfaces/formats.md#jsoneachrow).
- `'XML'` — Similarly to [XML](../../interfaces/formats.md#xml).
- `'Raw'` — Extracts subpatterns as a whole, no escaping rules, similarly to [TSVRaw](../../interfaces/formats.md#tabseparatedraw).
- `'Escaped'` — Similarly to [TSV](../../interfaces/formats.md/#tabseparated).
- `'Quoted'` — Similarly to [Values](../../interfaces/formats.md/#data-format-values).
- `'CSV'` — Similarly to [CSV](../../interfaces/formats.md/#csv).
- `'JSON'` — Similarly to [JSONEachRow](../../interfaces/formats.md/#jsoneachrow).
- `'XML'` — Similarly to [XML](../../interfaces/formats.md/#xml).
- `'Raw'` — Extracts subpatterns as a whole, no escaping rules, similarly to [TSVRaw](../../interfaces/formats.md/#tabseparatedraw).
Default value: `'Escaped'`.
### format_custom_field_delimiter {#format_custom_field_delimiter}
Sets the character that is interpreted as a delimiter between the fields for [CustomSeparated](../../interfaces/formats.md#format-customseparated) data format.
Sets the character that is interpreted as a delimiter between the fields for [CustomSeparated](../../interfaces/formats.md/#format-customseparated) data format.
Default value: `'\t'`.
### format_custom_row_before_delimiter {#format_custom_row_before_delimiter}
Sets the character that is interpreted as a delimiter before the field of the first column for [CustomSeparated](../../interfaces/formats.md#format-customseparated) data format.
Sets the character that is interpreted as a delimiter before the field of the first column for [CustomSeparated](../../interfaces/formats.md/#format-customseparated) data format.
Default value: `''`.
### format_custom_row_after_delimiter {#format_custom_row_after_delimiter}
Sets the character that is interpreted as a delimiter after the field of the last column for [CustomSeparated](../../interfaces/formats.md#format-customseparated) data format.
Sets the character that is interpreted as a delimiter after the field of the last column for [CustomSeparated](../../interfaces/formats.md/#format-customseparated) data format.
Default value: `'\n'`.
### format_custom_row_between_delimiter {#format_custom_row_between_delimiter}
Sets the character that is interpreted as a delimiter between the rows for [CustomSeparated](../../interfaces/formats.md#format-customseparated) data format.
Sets the character that is interpreted as a delimiter between the rows for [CustomSeparated](../../interfaces/formats.md/#format-customseparated) data format.
Default value: `''`.
### format_custom_result_before_delimiter {#format_custom_result_before_delimiter}
Sets the character that is interpreted as a prefix before the result set for [CustomSeparated](../../interfaces/formats.md#format-customseparated) data format.
Sets the character that is interpreted as a prefix before the result set for [CustomSeparated](../../interfaces/formats.md/#format-customseparated) data format.
Default value: `''`.
### format_custom_result_after_delimiter {#format_custom_result_after_delimiter}
Sets the character that is interpreted as a suffix after the result set for [CustomSeparated](../../interfaces/formats.md#format-customseparated) data format.
Sets the character that is interpreted as a suffix after the result set for [CustomSeparated](../../interfaces/formats.md/#format-customseparated) data format.
Default value: `''`.
@ -4727,12 +4738,12 @@ Field escaping rule.
Possible values:
- `'Escaped'` — Similarly to [TSV](../../interfaces/formats.md#tabseparated).
- `'Quoted'` — Similarly to [Values](../../interfaces/formats.md#data-format-values).
- `'CSV'` — Similarly to [CSV](../../interfaces/formats.md#csv).
- `'JSON'` — Similarly to [JSONEachRow](../../interfaces/formats.md#jsoneachrow).
- `'XML'` — Similarly to [XML](../../interfaces/formats.md#xml).
- `'Raw'` — Extracts subpatterns as a whole, no escaping rules, similarly to [TSVRaw](../../interfaces/formats.md#tabseparatedraw).
- `'Escaped'` — Similarly to [TSV](../../interfaces/formats.md/#tabseparated).
- `'Quoted'` — Similarly to [Values](../../interfaces/formats.md/#data-format-values).
- `'CSV'` — Similarly to [CSV](../../interfaces/formats.md/#csv).
- `'JSON'` — Similarly to [JSONEachRow](../../interfaces/formats.md/#jsoneachrow).
- `'XML'` — Similarly to [XML](../../interfaces/formats.md/#xml).
- `'Raw'` — Extracts subpatterns as a whole, no escaping rules, similarly to [TSVRaw](../../interfaces/formats.md/#tabseparatedraw).
Default value: `Raw`.
@ -4746,7 +4757,7 @@ Disabled by default.
### format_capn_proto_enum_comparising_mode {#format_capn_proto_enum_comparising_mode}
Determines how to map ClickHouse `Enum` data type and [CapnProto](../../interfaces/formats.md#capnproto) `Enum` data type from schema.
Determines how to map ClickHouse `Enum` data type and [CapnProto](../../interfaces/formats.md/#capnproto) `Enum` data type from schema.
Possible values:

18
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@ -7,13 +7,13 @@ title: "External Disks for Storing Data"
Data, processed in ClickHouse, is usually stored in the local file system — on the same machine with the ClickHouse server. That requires large-capacity disks, which can be expensive enough. To avoid that you can store the data remotely — on [Amazon S3](https://aws.amazon.com/s3/) disks or in the Hadoop Distributed File System ([HDFS](https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/HdfsDesign.html)).
To work with data stored on `Amazon S3` disks use [S3](../engines/table-engines/integrations/s3.md) table engine, and to work with data in the Hadoop Distributed File System — [HDFS](../engines/table-engines/integrations/hdfs.md) table engine.
To work with data stored on `Amazon S3` disks use [S3](/docs/en/engines/table-engines/integrations/s3.md) table engine, and to work with data in the Hadoop Distributed File System — [HDFS](/docs/en/engines/table-engines/integrations/hdfs.md) table engine.
To load data from a web server with static files use a disk with type [web](#storing-data-on-webserver).
## Configuring HDFS {#configuring-hdfs}
[MergeTree](../engines/table-engines/mergetree-family/mergetree.md) and [Log](../engines/table-engines/log-family/log.md) family table engines can store data to HDFS using a disk with type `HDFS`.
[MergeTree](/docs/en/engines/table-engines/mergetree-family/mergetree.md) and [Log](/docs/en/engines/table-engines/log-family/log.md) family table engines can store data to HDFS using a disk with type `HDFS`.
Configuration markup:
@ -53,7 +53,7 @@ Optional parameters:
## Using Virtual File System for Data Encryption {#encrypted-virtual-file-system}
You can encrypt the data stored on [S3](../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-s3), or [HDFS](#configuring-hdfs) external disks, or on a local disk. To turn on the encryption mode, in the configuration file you must define a disk with the type `encrypted` and choose a disk on which the data will be saved. An `encrypted` disk ciphers all written files on the fly, and when you read files from an `encrypted` disk it deciphers them automatically. So you can work with an `encrypted` disk like with a normal one.
You can encrypt the data stored on [S3](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-s3), or [HDFS](#configuring-hdfs) external disks, or on a local disk. To turn on the encryption mode, in the configuration file you must define a disk with the type `encrypted` and choose a disk on which the data will be saved. An `encrypted` disk ciphers all written files on the fly, and when you read files from an `encrypted` disk it deciphers them automatically. So you can work with an `encrypted` disk like with a normal one.
Example of disk configuration:
@ -80,14 +80,14 @@ Required parameters:
- `type` — `encrypted`. Otherwise the encrypted disk is not created.
- `disk` — Type of disk for data storage.
- `key` — The key for encryption and decryption. Type: [Uint64](../sql-reference/data-types/int-uint.md). You can use `key_hex` parameter to encrypt in hexadecimal form.
- `key` — The key for encryption and decryption. Type: [Uint64](/docs/en/sql-reference/data-types/int-uint.md). You can use `key_hex` parameter to encrypt in hexadecimal form.
You can specify multiple keys using the `id` attribute (see example above).
Optional parameters:
- `path` — Path to the location on the disk where the data will be saved. If not specified, the data will be saved in the root directory.
- `current_key_id` — The key used for encryption. All the specified keys can be used for decryption, and you can always switch to another key while maintaining access to previously encrypted data.
- `algorithm` — [Algorithm](../sql-reference/statements/create/table.md#create-query-encryption-codecs) for encryption. Possible values: `AES_128_CTR`, `AES_192_CTR` or `AES_256_CTR`. Default value: `AES_128_CTR`. The key length depends on the algorithm: `AES_128_CTR` — 16 bytes, `AES_192_CTR` — 24 bytes, `AES_256_CTR` — 32 bytes.
- `algorithm` — [Algorithm](/docs/en/sql-reference/statements/create/table.md/#create-query-encryption-codecs) for encryption. Possible values: `AES_128_CTR`, `AES_192_CTR` or `AES_256_CTR`. Default value: `AES_128_CTR`. The key length depends on the algorithm: `AES_128_CTR` — 16 bytes, `AES_192_CTR` — 24 bytes, `AES_256_CTR` — 32 bytes.
Example of disk configuration:
@ -265,9 +265,9 @@ Cache profile events:
There is a tool `clickhouse-static-files-uploader`, which prepares a data directory for a given table (`SELECT data_paths FROM system.tables WHERE name = 'table_name'`). For each table you need, you get a directory of files. These files can be uploaded to, for example, a web server with static files. After this preparation, you can load this table into any ClickHouse server via `DiskWeb`.
This is a read-only disk. Its data is only read and never modified. A new table is loaded to this disk via `ATTACH TABLE` query (see example below). Local disk is not actually used, each `SELECT` query will result in a `http` request to fetch required data. All modification of the table data will result in an exception, i.e. the following types of queries are not allowed: [CREATE TABLE](../sql-reference/statements/create/table.md), [ALTER TABLE](../sql-reference/statements/alter/index.md), [RENAME TABLE](../sql-reference/statements/rename.md#misc_operations-rename_table), [DETACH TABLE](../sql-reference/statements/detach.md) and [TRUNCATE TABLE](../sql-reference/statements/truncate.md).
This is a read-only disk. Its data is only read and never modified. A new table is loaded to this disk via `ATTACH TABLE` query (see example below). Local disk is not actually used, each `SELECT` query will result in a `http` request to fetch required data. All modification of the table data will result in an exception, i.e. the following types of queries are not allowed: [CREATE TABLE](/docs/en/sql-reference/statements/create/table.md), [ALTER TABLE](/docs/en/sql-reference/statements/alter/index.md), [RENAME TABLE](/docs/en/sql-reference/statements/rename.md/#misc_operations-rename_table), [DETACH TABLE](/docs/en/sql-reference/statements/detach.md) and [TRUNCATE TABLE](/docs/en/sql-reference/statements/truncate.md).
Web server storage is supported only for the [MergeTree](../engines/table-engines/mergetree-family/mergetree.md) and [Log](../engines/table-engines/log-family/log.md) engine families. To access the data stored on a `web` disk, use the [storage_policy](../engines/table-engines/mergetree-family/mergetree.md#terms) setting when executing the query. For example, `ATTACH TABLE table_web UUID '{}' (id Int32) ENGINE = MergeTree() ORDER BY id SETTINGS storage_policy = 'web'`.
Web server storage is supported only for the [MergeTree](/docs/en/engines/table-engines/mergetree-family/mergetree.md) and [Log](/docs/en/engines/table-engines/log-family/log.md) engine families. To access the data stored on a `web` disk, use the [storage_policy](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#terms) setting when executing the query. For example, `ATTACH TABLE table_web UUID '{}' (id Int32) ENGINE = MergeTree() ORDER BY id SETTINGS storage_policy = 'web'`.
A ready test case. You need to add this configuration to config:
@ -451,7 +451,7 @@ Optional parameters:
- `remote_fs_read_backoff_threashold` — The maximum wait time when trying to read data for remote disk. Default value: `10000` seconds.
- `remote_fs_read_backoff_max_tries` — The maximum number of attempts to read with backoff. Default value: `5`.
If a query fails with an exception `DB:Exception Unreachable URL`, then you can try to adjust the settings: [http_connection_timeout](../operations/settings/settings.md#http_connection_timeout), [http_receive_timeout](../operations/settings/settings.md#http_receive_timeout), [keep_alive_timeout](../operations/server-configuration-parameters/settings.md#keep-alive-timeout).
If a query fails with an exception `DB:Exception Unreachable URL`, then you can try to adjust the settings: [http_connection_timeout](/docs/en/operations/settings/settings.md/#http_connection_timeout), [http_receive_timeout](/docs/en/operations/settings/settings.md/#http_receive_timeout), [keep_alive_timeout](/docs/en/operations/server-configuration-parameters/settings.md/#keep-alive-timeout).
To get files for upload run:
`clickhouse static-files-disk-uploader --metadata-path <path> --output-dir <dir>` (`--metadata-path` can be found in query `SELECT data_paths FROM system.tables WHERE name = 'table_name'`).
@ -460,7 +460,7 @@ When loading files by `endpoint`, they must be loaded into `<endpoint>/store/` p
If URL is not reachable on disk load when the server is starting up tables, then all errors are caught. If in this case there were errors, tables can be reloaded (become visible) via `DETACH TABLE table_name` -> `ATTACH TABLE table_name`. If metadata was successfully loaded at server startup, then tables are available straight away.
Use [http_max_single_read_retries](../operations/settings/settings.md#http-max-single-read-retries) setting to limit the maximum number of retries during a single HTTP read.
Use [http_max_single_read_retries](/docs/en/operations/settings/settings.md/#http-max-single-read-retries) setting to limit the maximum number of retries during a single HTTP read.
## Zero-copy Replication (not ready for production) {#zero-copy}

4
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@ -7,8 +7,8 @@ Contains information about stack traces for fatal errors. The table does not exi
Columns:
- `event_date` ([Datetime](../../sql-reference/data-types/datetime.md)) — Date of the event.
- `event_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — Time of the event.
- `event_date` ([DateTime](../../sql-reference/data-types/datetime.md)) — Date of the event.
- `event_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — Time of the event.
- `timestamp_ns` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Timestamp of the event with nanoseconds.
- `signal` ([Int32](../../sql-reference/data-types/int-uint.md)) — Signal number.
- `thread_id` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Thread ID.

4
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@ -3,7 +3,7 @@ slug: /en/operations/system-tables/dictionaries
---
# dictionaries
Contains information about [external dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md).
Contains information about [dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md).
Columns:
@ -33,7 +33,7 @@ Columns:
- `lifetime_min` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Minimum [lifetime](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-lifetime.md) of the dictionary in memory, after which ClickHouse tries to reload the dictionary (if `invalidate_query` is set, then only if it has changed). Set in seconds.
- `lifetime_max` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Maximum [lifetime](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-lifetime.md) of the dictionary in memory, after which ClickHouse tries to reload the dictionary (if `invalidate_query` is set, then only if it has changed). Set in seconds.
- `loading_start_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — Start time for loading the dictionary.
- `last_successful_update_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — End time for loading or updating the dictionary. Helps to monitor some troubles with external sources and investigate causes.
- `last_successful_update_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — End time for loading or updating the dictionary. Helps to monitor some troubles with dictionary sources and investigate the causes.
- `loading_duration` ([Float32](../../sql-reference/data-types/float.md)) — Duration of a dictionary loading.
- `last_exception` ([String](../../sql-reference/data-types/string.md)) — Text of the error that occurs when creating or reloading the dictionary if the dictionary couldn’t be created.
- `comment` ([String](../../sql-reference/data-types/string.md)) — Text of the comment to dictionary.

4
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@ -1,7 +1,8 @@
---
slug: /en/operations/system-tables/
sidebar_position: 52
sidebar_label: System Tables
sidebar_label: Overview
pagination_next: 'en/operations/system-tables/asynchronous_metric_log'
---
# System Tables
@ -72,4 +73,3 @@ If procfs is supported and enabled on the system, ClickHouse server collects the
- `OSReadBytes`
- `OSWriteBytes`
[Original article](https://clickhouse.com/docs/en/operations/system-tables/) <!--hide-->

34
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@ -3,31 +3,31 @@ slug: /en/operations/system-tables/mutations
---
# mutations
The table contains information about [mutations](../../sql-reference/statements/alter/index.md#mutations) of [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) tables and their progress. Each mutation command is represented by a single row.
The table contains information about [mutations](/docs/en/sql-reference/statements/alter/index.md/#mutations) of [MergeTree](/docs/en/engines/table-engines/mergetree-family/mergetree.md) tables and their progress. Each mutation command is represented by a single row.
Columns:
- `database` ([String](../../sql-reference/data-types/string.md)) — The name of the database to which the mutation was applied.
- `database` ([String](/docs/en/sql-reference/data-types/string.md)) — The name of the database to which the mutation was applied.
- `table` ([String](../../sql-reference/data-types/string.md)) — The name of the table to which the mutation was applied.
- `table` ([String](/docs/en/sql-reference/data-types/string.md)) — The name of the table to which the mutation was applied.
- `mutation_id` ([String](../../sql-reference/data-types/string.md)) — The ID of the mutation. For replicated tables these IDs correspond to znode names in the `<table_path_in_clickhouse_keeper>/mutations/` directory in ClickHouse Keeper. For non-replicated tables the IDs correspond to file names in the data directory of the table.
- `mutation_id` ([String](/docs/en/sql-reference/data-types/string.md)) — The ID of the mutation. For replicated tables these IDs correspond to znode names in the `<table_path_in_clickhouse_keeper>/mutations/` directory in ClickHouse Keeper. For non-replicated tables the IDs correspond to file names in the data directory of the table.
- `command` ([String](../../sql-reference/data-types/string.md)) — The mutation command string (the part of the query after `ALTER TABLE [db.]table`).
- `command` ([String](/docs/en/sql-reference/data-types/string.md)) — The mutation command string (the part of the query after `ALTER TABLE [db.]table`).
- `create_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — Date and time when the mutation command was submitted for execution.
- `create_time` ([DateTime](/docs/en/sql-reference/data-types/datetime.md)) — Date and time when the mutation command was submitted for execution.
- `block_numbers.partition_id` ([Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md))) — For mutations of replicated tables, the array contains the partitions' IDs (one record for each partition). For mutations of non-replicated tables the array is empty.
- `block_numbers.partition_id` ([Array](/docs/en/sql-reference/data-types/array.md)([String](/docs/en/sql-reference/data-types/string.md))) — For mutations of replicated tables, the array contains the partitions' IDs (one record for each partition). For mutations of non-replicated tables the array is empty.
- `block_numbers.number` ([Array](../../sql-reference/data-types/array.md)([Int64](../../sql-reference/data-types/int-uint.md))) — For mutations of replicated tables, the array contains one record for each partition, with the block number that was acquired by the mutation. Only parts that contain blocks with numbers less than this number will be mutated in the partition.
- `block_numbers.number` ([Array](/docs/en/sql-reference/data-types/array.md)([Int64](/docs/en/sql-reference/data-types/int-uint.md))) — For mutations of replicated tables, the array contains one record for each partition, with the block number that was acquired by the mutation. Only parts that contain blocks with numbers less than this number will be mutated in the partition.
In non-replicated tables, block numbers in all partitions form a single sequence. This means that for mutations of non-replicated tables, the column will contain one record with a single block number acquired by the mutation.
- `parts_to_do_names` ([Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md))) — An array of names of data parts that need to be mutated for the mutation to complete.
- `parts_to_do_names` ([Array](/docs/en/sql-reference/data-types/array.md)([String](/docs/en/sql-reference/data-types/string.md))) — An array of names of data parts that need to be mutated for the mutation to complete.
- `parts_to_do` ([Int64](../../sql-reference/data-types/int-uint.md)) — The number of data parts that need to be mutated for the mutation to complete.
- `parts_to_do` ([Int64](/docs/en/sql-reference/data-types/int-uint.md)) — The number of data parts that need to be mutated for the mutation to complete.
- `is_done` ([UInt8](../../sql-reference/data-types/int-uint.md)) — The flag whether the mutation is done or not. Possible values:
- `is_done` ([UInt8](/docs/en/sql-reference/data-types/int-uint.md)) — The flag whether the mutation is done or not. Possible values:
- `1` if the mutation is completed,
- `0` if the mutation is still in process.
@ -37,16 +37,16 @@ Even if `parts_to_do = 0` it is possible that a mutation of a replicated table i
If there were problems with mutating some data parts, the following columns contain additional information:
- `latest_failed_part` ([String](../../sql-reference/data-types/string.md)) — The name of the most recent part that could not be mutated.
- `latest_failed_part` ([String](/docs/en/sql-reference/data-types/string.md)) — The name of the most recent part that could not be mutated.
- `latest_fail_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — The date and time of the most recent part mutation failure.
- `latest_fail_time` ([DateTime](/docs/en/sql-reference/data-types/datetime.md)) — The date and time of the most recent part mutation failure.
- `latest_fail_reason` ([String](../../sql-reference/data-types/string.md)) — The exception message that caused the most recent part mutation failure.
- `latest_fail_reason` ([String](/docs/en/sql-reference/data-types/string.md)) — The exception message that caused the most recent part mutation failure.
**See Also**
- [Mutations](../../sql-reference/statements/alter/index.md#mutations)
- [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) table engine
- [ReplicatedMergeTree](../../engines/table-engines/mergetree-family/replication.md) family
- [Mutations](/docs/en/sql-reference/statements/alter/index.md/#mutations)
- [MergeTree](/docs/en/engines/table-engines/mergetree-family/mergetree.md) table engine
- [ReplicatedMergeTree](/docs/en/engines/table-engines/mergetree-family/replication.md) family
[Original article](https://clickhouse.com/docs/en/operations/system-tables/mutations) <!--hide-->

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@ -9,7 +9,7 @@ Each row describes one data part.
Columns:
- `partition` ([String](../../sql-reference/data-types/string.md)) – The partition name. To learn what a partition is, see the description of the [ALTER](../../sql-reference/statements/alter/index.md#query_language_queries_alter) query.
- `partition` ([String](../../sql-reference/data-types/string.md)) – The partition name. To learn what a partition is, see the description of the [ALTER](../../sql-reference/statements/alter/index.md/#query_language_queries_alter) query.
Formats:
@ -75,7 +75,7 @@ Columns:
- `primary_key_bytes_in_memory_allocated` ([UInt64](../../sql-reference/data-types/int-uint.md)) – The amount of memory (in bytes) reserved for primary key values.
- `is_frozen` ([UInt8](../../sql-reference/data-types/int-uint.md)) – Flag that shows that a partition data backup exists. 1, the backup exists. 0, the backup does not exist. For more details, see [FREEZE PARTITION](../../sql-reference/statements/alter/partition.md#alter_freeze-partition)
- `is_frozen` ([UInt8](../../sql-reference/data-types/int-uint.md)) – Flag that shows that a partition data backup exists. 1, the backup exists. 0, the backup does not exist. For more details, see [FREEZE PARTITION](../../sql-reference/statements/alter/partition.md/#alter_freeze-partition)
- `database` ([String](../../sql-reference/data-types/string.md)) – Name of the database.
@ -87,25 +87,25 @@ Columns:
- `disk_name` ([String](../../sql-reference/data-types/string.md)) – Name of a disk that stores the data part.
- `hash_of_all_files` ([String](../../sql-reference/data-types/string.md)) – [sipHash128](../../sql-reference/functions/hash-functions.md#hash_functions-siphash128) of compressed files.
- `hash_of_all_files` ([String](../../sql-reference/data-types/string.md)) – [sipHash128](../../sql-reference/functions/hash-functions.md/#hash_functions-siphash128) of compressed files.
- `hash_of_uncompressed_files` ([String](../../sql-reference/data-types/string.md)) – [sipHash128](../../sql-reference/functions/hash-functions.md#hash_functions-siphash128) of uncompressed files (files with marks, index file etc.).
- `hash_of_uncompressed_files` ([String](../../sql-reference/data-types/string.md)) – [sipHash128](../../sql-reference/functions/hash-functions.md/#hash_functions-siphash128) of uncompressed files (files with marks, index file etc.).
- `uncompressed_hash_of_compressed_files` ([String](../../sql-reference/data-types/string.md)) – [sipHash128](../../sql-reference/functions/hash-functions.md#hash_functions-siphash128) of data in the compressed files as if they were uncompressed.
- `uncompressed_hash_of_compressed_files` ([String](../../sql-reference/data-types/string.md)) – [sipHash128](../../sql-reference/functions/hash-functions.md/#hash_functions-siphash128) of data in the compressed files as if they were uncompressed.
- `delete_ttl_info_min` ([DateTime](../../sql-reference/data-types/datetime.md)) — The minimum value of the date and time key for [TTL DELETE rule](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-ttl).
- `delete_ttl_info_min` ([DateTime](../../sql-reference/data-types/datetime.md)) — The minimum value of the date and time key for [TTL DELETE rule](../../engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-ttl).
- `delete_ttl_info_max` ([DateTime](../../sql-reference/data-types/datetime.md)) — The maximum value of the date and time key for [TTL DELETE rule](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-ttl).
- `delete_ttl_info_max` ([DateTime](../../sql-reference/data-types/datetime.md)) — The maximum value of the date and time key for [TTL DELETE rule](../../engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-ttl).
- `move_ttl_info.expression` ([Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md))) — Array of expressions. Each expression defines a [TTL MOVE rule](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-ttl).
- `move_ttl_info.expression` ([Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md))) — Array of expressions. Each expression defines a [TTL MOVE rule](../../engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-ttl).
:::warning
The `move_ttl_info.expression` array is kept mostly for backward compatibility, now the simpliest way to check `TTL MOVE` rule is to use the `move_ttl_info.min` and `move_ttl_info.max` fields.
:::
- `move_ttl_info.min` ([Array](../../sql-reference/data-types/array.md)([DateTime](../../sql-reference/data-types/datetime.md))) — Array of date and time values. Each element describes the minimum key value for a [TTL MOVE rule](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-ttl).
- `move_ttl_info.min` ([Array](../../sql-reference/data-types/array.md)([DateTime](../../sql-reference/data-types/datetime.md))) — Array of date and time values. Each element describes the minimum key value for a [TTL MOVE rule](../../engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-ttl).
- `move_ttl_info.max` ([Array](../../sql-reference/data-types/array.md)([DateTime](../../sql-reference/data-types/datetime.md))) — Array of date and time values. Each element describes the maximum key value for a [TTL MOVE rule](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-ttl).
- `move_ttl_info.max` ([Array](../../sql-reference/data-types/array.md)([DateTime](../../sql-reference/data-types/datetime.md))) — Array of date and time values. Each element describes the maximum key value for a [TTL MOVE rule](../../engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-ttl).
- `bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) – Alias for `bytes_on_disk`.
@ -166,6 +166,6 @@ move_ttl_info.max: []
**See Also**
- [MergeTree family](../../engines/table-engines/mergetree-family/mergetree.md)
- [TTL for Columns and Tables](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-ttl)
- [TTL for Columns and Tables](../../engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-ttl)
[Original article](https://clickhouse.com/docs/en/operations/system-tables/parts) <!--hide-->

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@ -9,7 +9,7 @@ Each row describes one data part.
Columns:
- `partition` ([String](../../sql-reference/data-types/string.md)) — The partition name. To learn what a partition is, see the description of the [ALTER](../../sql-reference/statements/alter/index.md#query_language_queries_alter) query.
- `partition` ([String](../../sql-reference/data-types/string.md)) — The partition name. To learn what a partition is, see the description of the [ALTER](../../sql-reference/statements/alter/index.md/#query_language_queries_alter) query.
Formats:

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@ -29,7 +29,7 @@ Columns:
- `MUTATE_PART` — Apply one or several mutations to the part.
- `ALTER_METADATA` — Apply alter modification according to global /metadata and /columns paths.
- `create_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — Date and time when the task was submitted for execution.
- `create_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — Date and time when the task was submitted for execution.
- `required_quorum` ([UInt32](../../sql-reference/data-types/int-uint.md)) — The number of replicas waiting for the task to complete with confirmation of completion. This column is only relevant for the `GET_PARTS` task.
@ -47,13 +47,13 @@ Columns:
- `last_exception` ([String](../../sql-reference/data-types/string.md)) — Text message about the last error that occurred (if any).
- `last_attempt_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — Date and time when the task was last attempted.
- `last_attempt_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — Date and time when the task was last attempted.
- `num_postponed` ([UInt32](../../sql-reference/data-types/int-uint.md)) — The number of postponed tasks.
- `postpone_reason` ([String](../../sql-reference/data-types/string.md)) — The reason why the task was postponed.
- `last_postpone_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — Date and time when the task was last postponed.
- `last_postpone_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — Date and time when the task was last postponed.
- `merge_type` ([String](../../sql-reference/data-types/string.md)) — Type of the current merge. Empty if it's a mutation.

5
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@ -1,10 +1,11 @@
---
slug: /en/operations/utilities/
sidebar_position: 56
sidebar_label: Utilities
sidebar_label: Overview
pagination_next: 'en/operations/utilities/clickhouse-copier'
---
# ClickHouse Utility
# ClickHouse Utilities
- [clickhouse-local](../../operations/utilities/clickhouse-local.md) — Allows running SQL queries on data without starting the ClickHouse server, similar to how `awk` does this.
- [clickhouse-copier](../../operations/utilities/clickhouse-copier.md) — Copies (and reshards) data from one cluster to another cluster.

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@ -6,7 +6,7 @@ sidebar_label: Date32
# Date32
A date. Supports the date range same with [Datetime64](../../sql-reference/data-types/datetime64.md). Stored in four bytes as the number of days since 1900-01-01. Allows storing values till 2299-12-31.
A date. Supports the date range same with [DateTime64](../../sql-reference/data-types/datetime64.md). Stored in four bytes as the number of days since 1900-01-01. Allows storing values till 2299-12-31.
**Examples**

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@ -4,7 +4,7 @@ sidebar_position: 48
sidebar_label: DateTime
---
# Datetime
# DateTime
Allows to store an instant in time, that can be expressed as a calendar date and a time of a day.

2
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@ -4,7 +4,7 @@ sidebar_position: 49
sidebar_label: DateTime64
---
# Datetime64
# DateTime64
Allows to store an instant in time, that can be expressed as a calendar date and a time of a day, with defined sub-second precision

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@ -1,8 +1,8 @@
position: 37
label: 'External Dictionaries'
label: 'Dictionaries'
collapsible: true
collapsed: true
link:
type: generated-index
title: External Dictionaries
title: Dictionaries
slug: /en/sql-reference/dictionaries/external-dictionaries

4
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@ -0,0 +1,4 @@
:::tip
If you are using a dictionary with ClickHouse Cloud please use the DDL query option to create your dictionaries, and create your dictionary as user `default`.
Also, verify the list of supported dictionary sources in the [Cloud Compatibility guide](/docs/en/whats-new/cloud-capabilities.md).
:::

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@ -3,6 +3,7 @@ slug: /en/sql-reference/dictionaries/external-dictionaries/external-dicts-dict-l
sidebar_position: 41
sidebar_label: Storing Dictionaries in Memory
---
import CloudDetails from '@site/docs/en/sql-reference/dictionaries/external-dictionaries/_snippet_dictionary_in_cloud.md';
# Storing Dictionaries in Memory
@ -22,7 +23,9 @@ ClickHouse generates an exception for errors with dictionaries. Examples of erro
- The dictionary being accessed could not be loaded.
- Error querying a `cached` dictionary.
You can view the list of external dictionaries and their statuses in the [system.dictionaries](../../../operations/system-tables/dictionaries.md) table.
You can view the list of dictionaries and their statuses in the [system.dictionaries](../../../operations/system-tables/dictionaries.md) table.
<CloudDetails />
The configuration looks like this:

3
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@ -3,6 +3,7 @@ slug: /en/sql-reference/dictionaries/external-dictionaries/external-dicts-dict-l
sidebar_position: 42
sidebar_label: Dictionary Updates
---
import CloudDetails from '@site/docs/en/sql-reference/dictionaries/external-dictionaries/_snippet_dictionary_in_cloud.md';
# Dictionary Updates
@ -12,6 +13,8 @@ Dictionary updates (other than loading for first use) do not block queries. Duri
Example of settings:
<CloudDetails />
``` xml
<dictionary>
...

5
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@ -4,12 +4,15 @@ sidebar_position: 46
sidebar_label: Polygon Dictionaries With Grids
title: "Polygon dictionaries"
---
import CloudDetails from '@site/docs/en/sql-reference/dictionaries/external-dictionaries/_snippet_dictionary_in_cloud.md';
Polygon dictionaries allow you to efficiently search for the polygon containing specified points.
For example: defining a city area by geographical coordinates.
Example of a polygon dictionary configuration:
<CloudDetails />
``` xml
<dictionary>
<structure>
@ -78,7 +81,7 @@ To respond to the query, there is a corresponding cell, and the index for the po
- `POLYGON`. Synonym to `POLYGON_INDEX_CELL`.
Dictionary queries are carried out using standard [functions](../../../sql-reference/functions/ext-dict-functions.md) for working with external dictionaries.
Dictionary queries are carried out using standard [functions](../../../sql-reference/functions/ext-dict-functions.md) for working with dictionaries.
An important difference is that here the keys will be the points for which you want to find the polygon containing them.
**Example**

23
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@ -1,12 +1,15 @@
---
slug: /en/sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources
sidebar_position: 43
sidebar_label: Sources of External Dictionaries
sidebar_label: Dictionary Sources
---
import CloudDetails from '@site/docs/en/sql-reference/dictionaries/external-dictionaries/_snippet_dictionary_in_cloud.md';
# Sources of External Dictionaries
# Dictionary Sources
An external dictionary can be connected to ClickHouse from many different sources.
<CloudDetails />
A dictionary can be connected to ClickHouse from many different sources.
If the dictionary is configured using an xml-file, the configuration looks like this:
@ -65,13 +68,13 @@ Types of sources (`source_type`):
- [Executable Pool](#dicts-external_dicts_dict_sources-executable_pool)
- [HTTP(s)](#dicts-external_dicts_dict_sources-http)
- DBMS
- [ODBC](#dicts-external_dicts_dict_sources-odbc)
- [MySQL](#dicts-external_dicts_dict_sources-mysql)
- [ClickHouse](#dicts-external_dicts_dict_sources-clickhouse)
- [MongoDB](#dicts-external_dicts_dict_sources-mongodb)
- [Redis](#dicts-external_dicts_dict_sources-redis)
- [Cassandra](#dicts-external_dicts_dict_sources-cassandra)
- [PostgreSQL](#dicts-external_dicts_dict_sources-postgresql)
- [ODBC](#odbc)
- [MySQL](#mysql)
- [ClickHouse](#clickhouse)
- [MongoDB](#mongodb)
- [Redis](#redis)
- [Cassandra](#cassandra)
- [PostgreSQL](#postgresql)
## Local File

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@ -3,9 +3,12 @@ slug: /en/sql-reference/dictionaries/external-dictionaries/external-dicts-dict-s
sidebar_position: 44
sidebar_label: Dictionary Key and Fields
---
import CloudDetails from '@site/docs/en/sql-reference/dictionaries/external-dictionaries/_snippet_dictionary_in_cloud.md';
# Dictionary Key and Fields
<CloudDetails />
The `structure` clause describes the dictionary key and fields available for queries.
XML description:
@ -171,5 +174,5 @@ Configuration fields:
**See Also**
- [Functions for working with external dictionaries](../../../sql-reference/functions/ext-dict-functions.md).
- [Functions for working with dictionaries](../../../sql-reference/functions/ext-dict-functions.md).

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@ -1,10 +1,13 @@
---
slug: /en/sql-reference/dictionaries/external-dictionaries/external-dicts-dict
sidebar_position: 40
sidebar_label: Configuring an External Dictionary
sidebar_label: Configuring a Dictionary
---
import CloudDetails from '@site/docs/en/sql-reference/dictionaries/external-dictionaries/_snippet_dictionary_in_cloud.md';
# Configuring an External Dictionary
# Configuring a Dictionary
<CloudDetails />
If dictionary is configured using xml file, than dictionary configuration has the following structure:

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@ -3,18 +3,21 @@ slug: /en/sql-reference/dictionaries/external-dictionaries/external-dicts
sidebar_position: 39
sidebar_label: General Description
---
import CloudDetails from '@site/docs/en/sql-reference/dictionaries/external-dictionaries/_snippet_dictionary_in_cloud.md';
# External Dictionaries
# Dictionaries
You can add your own dictionaries from various data sources. The data source for a dictionary can be a local text or executable file, an HTTP(s) resource, or another DBMS. For more information, see “[Sources for external dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md)”.
<CloudDetails />
You can add your own dictionaries from various data sources. The source for a dictionary can be a ClickHouse table, a local text or executable file, an HTTP(s) resource, or another DBMS. For more information, see “[Dictionary Sources](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md)”.
ClickHouse:
- Fully or partially stores dictionaries in RAM.
- Periodically updates dictionaries and dynamically loads missing values. In other words, dictionaries can be loaded dynamically.
- Allows to create external dictionaries with xml files or [DDL queries](../../../sql-reference/statements/create/dictionary.md).
- Allows creating dictionaries with xml files or [DDL queries](../../../sql-reference/statements/create/dictionary.md).
The configuration of external dictionaries can be located in one or more xml-files. The path to the configuration is specified in the [dictionaries_config](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_config) parameter.
The configuration of dictionaries can be located in one or more xml-files. The path to the configuration is specified in the [dictionaries_config](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_config) parameter.
Dictionaries can be loaded at server startup or at first use, depending on the [dictionaries_lazy_load](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_lazy_load) setting.
@ -24,6 +27,20 @@ The [dictionaries](../../../operations/system-tables/dictionaries.md#system_tabl
- Configuration parameters.
- Metrics like amount of RAM allocated for the dictionary or a number of queries since the dictionary was successfully loaded.
## Creating a dictionary with a DDL query
Dictionaries can be created with [DDL queries](../../../sql-reference/statements/create/dictionary.md), and this is the recommended method because with DDL created dictionaries:
- No additional records are added to server configuration files
- The dictionaries can be worked with as first-class entities, like tables or views
- Data can be read directly, using familiar SELECT rather than dictionary table functions
- The dictionaries can be easily renamed
## Creating a dictionary with a configuration file
:::note
Creating a dictionary with a configuration file is not applicable to ClickHouse Cloud. Please use DDL (see above), and create your dictionary as user `default`.
:::
The dictionary configuration file has the following format:
``` xml
@ -44,18 +61,17 @@ The dictionary configuration file has the following format:
You can [configure](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict.md) any number of dictionaries in the same file.
[DDL queries for dictionaries](../../../sql-reference/statements/create/dictionary.md) does not require any additional records in server configuration. They allow to work with dictionaries as first-class entities, like tables or views.
:::note
You can convert values for a small dictionary by describing it in a `SELECT` query (see the [transform](../../../sql-reference/functions/other-functions.md) function). This functionality is not related to external dictionaries.
You can convert values for a small dictionary by describing it in a `SELECT` query (see the [transform](../../../sql-reference/functions/other-functions.md) function). This functionality is not related to dictionaries.
:::
## See Also
- [Configuring an External Dictionary](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict.md)
- [Configuring a Dictionary](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict.md)
- [Storing Dictionaries in Memory](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-layout.md)
- [Dictionary Updates](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-lifetime.md)
- [Sources of External Dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md)
- [Dictionary Sources](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md)
- [Dictionary Key and Fields](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md)
- [Functions for Working with External Dictionaries](../../../sql-reference/functions/ext-dict-functions.md)
- [Functions for Working with Dictionaries](../../../sql-reference/functions/ext-dict-functions.md)

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@ -12,6 +12,6 @@ ClickHouse supports special functions for working with dictionaries that can be
ClickHouse supports:
- [Built-in dictionaries](../../sql-reference/dictionaries/internal-dicts.md#internal_dicts) with a specific [set of functions](../../sql-reference/functions/ym-dict-functions.md).
- [Plug-in (external) dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md#dicts-external-dicts) with a [set of functions](../../sql-reference/functions/ext-dict-functions.md).
- [Dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md#dicts-external-dicts) with a [set of functions](../../sql-reference/functions/ext-dict-functions.md).
- [Embedded dictionaries](../../sql-reference/dictionaries/internal-dicts.md#internal_dicts) with a specific [set of functions](../../sql-reference/functions/ym-dict-functions.md).

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@ -1,10 +1,13 @@
---
slug: /en/sql-reference/dictionaries/internal-dicts
sidebar_position: 39
sidebar_label: Internal Dictionaries
sidebar_label: Embedded Dictionaries
---
import SelfManaged from '@site/docs/en/_snippets/_self_managed_only_no_roadmap.md';
# Internal Dictionaries
# Embedded Dictionaries
<SelfManaged />
ClickHouse contains a built-in feature for working with a geobase.

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@ -65,6 +65,11 @@ An exception is thrown when dividing by zero or when dividing a minimal negative
Differs from [modulo](#modulo) in that it returns zero when the divisor is zero.
## positive_modulo(a, b)
Calculates the remainder when dividing `a` by `b`. Similar to function `modulo` except that `positive_modulo` always return non-negative number.
Notice that `positive_modulo` is 4-5 times slower than `modulo`. You should not use `positive_modulo` unless you want to get positive result and don't care about performance too much.
## negate(a), -a operator
Calculates a number with the reverse sign. The result is always signed.

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@ -550,7 +550,7 @@ Alias: `dateTrunc`.
- Value, truncated to the specified part of date.
Type: [Datetime](../../sql-reference/data-types/datetime.md).
Type: [DateTime](../../sql-reference/data-types/datetime.md).
**Example**
@ -881,7 +881,7 @@ now([timezone])
- Current date and time.
Type: [Datetime](../../sql-reference/data-types/datetime.md).
Type: [DateTime](../../sql-reference/data-types/datetime.md).
**Example**
@ -932,7 +932,7 @@ now64([scale], [timezone])
- Current date and time with sub-second precision.
Type: [Datetime64](../../sql-reference/data-types/datetime64.md).
Type: [DateTime64](../../sql-reference/data-types/datetime64.md).
**Example**
@ -968,7 +968,7 @@ nowInBlock([timezone])
- Current date and time at the moment of processing of each block of data.
Type: [Datetime](../../sql-reference/data-types/datetime.md).
Type: [DateTime](../../sql-reference/data-types/datetime.md).
**Example**

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@ -1,20 +1,20 @@
---
slug: /en/sql-reference/functions/ext-dict-functions
sidebar_position: 58
sidebar_label: External Dictionaries
sidebar_label: Dictionaries
---
# Functions for Working with Dictionaries
:::note
For dictionaries created with [DDL queries](../../sql-reference/statements/create/dictionary.md), the `dict_name` parameter must be fully specified, like `<database>.<dict_name>`. Otherwise, the current database is used.
:::
# Functions for Working with External Dictionaries
For information on connecting and configuring external dictionaries, see [External dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md).
For information on connecting and configuring dictionaries, see [Dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md).
## dictGet, dictGetOrDefault, dictGetOrNull
Retrieves values from an external dictionary.
Retrieves values from a dictionary.
``` sql
dictGet('dict_name', attr_names, id_expr)
@ -52,7 +52,7 @@ Create a text file `ext-dict-test.csv` containing the following:
The first column is `id`, the second column is `c1`.
Configure the external dictionary:
Configure the dictionary:
``` xml
<clickhouse>
@ -112,7 +112,7 @@ Create a text file `ext-dict-mult.csv` containing the following:
The first column is `id`, the second is `c1`, the third is `c2`.
Configure the external dictionary:
Configure the dictionary:
``` xml
<clickhouse>
@ -185,7 +185,7 @@ INSERT INTO range_key_dictionary_source_table VALUES(2, toDate('2019-05-20'), to
INSERT INTO range_key_dictionary_source_table VALUES(3, toDate('2019-05-20'), toDate('2019-05-20'), 'Third', 'Third');
```
Create the external dictionary:
Create the dictionary:
```sql
CREATE DICTIONARY range_key_dictionary
@ -226,7 +226,7 @@ Result:
**See Also**
- [External Dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md)
- [Dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md)
## dictHas

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@ -24,6 +24,11 @@ Returns a pseudo-random UInt64 number, evenly distributed among all UInt64-type
Uses a linear congruential generator.
## canonicalRand
The function generates pseudo random results with independent and identically distributed uniformly distributed values in [0, 1).
Non-deterministic. Return type is Float64.
## randConstant
Produces a constant column with a random value.

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@ -6,21 +6,22 @@ sidebar_label: Splitting and Merging Strings and Arrays
# Functions for Splitting and Merging Strings and Arrays
## splitByChar(separator, s)
## splitByChar(separator, s[, max_substrings])
Splits a string into substrings separated by a specified character. It uses a constant string `separator` which consisting of exactly one character.
Splits a string into substrings separated by a specified character. It uses a constant string `separator` which consists of exactly one character.
Returns an array of selected substrings. Empty substrings may be selected if the separator occurs at the beginning or end of the string, or if there are multiple consecutive separators.
**Syntax**
``` sql
splitByChar(separator, s)
splitByChar(separator, s[, max_substrings]))
```
**Arguments**
- `separator` — The separator which should contain exactly one character. [String](../../sql-reference/data-types/string.md).
- `s` — The string to split. [String](../../sql-reference/data-types/string.md).
- `max_substrings` — An optional `Int64` defaulting to 0. When `max_substrings` > 0, the returned substrings will be no more than `max_substrings`, otherwise the function will return as many substrings as possible.
**Returned value(s)**
@ -44,20 +45,22 @@ SELECT splitByChar(',', '1,2,3,abcde');
└─────────────────────────────────┘
```
## splitByString(separator, s)
## splitByString(separator, s[, max_substrings])
Splits a string into substrings separated by a string. It uses a constant string `separator` of multiple characters as the separator. If the string `separator` is empty, it will split the string `s` into an array of single characters.
**Syntax**
``` sql
splitByString(separator, s)
splitByString(separator, s[, max_substrings]))
```
**Arguments**
- `separator` — The separator. [String](../../sql-reference/data-types/string.md).
- `s` — The string to split. [String](../../sql-reference/data-types/string.md).
- `max_substrings` — An optional `Int64` defaulting to 0. When `max_substrings` > 0, the returned substrings will be no more than `max_substrings`, otherwise the function will return as many substrings as possible.
**Returned value(s)**
@ -91,20 +94,22 @@ SELECT splitByString('', 'abcde');
└────────────────────────────┘
```
## splitByRegexp(regexp, s)
## splitByRegexp(regexp, s[, max_substrings])
Splits a string into substrings separated by a regular expression. It uses a regular expression string `regexp` as the separator. If the `regexp` is empty, it will split the string `s` into an array of single characters. If no match is found for this regular expression, the string `s` won't be split.
**Syntax**
``` sql
splitByRegexp(regexp, s)
splitByRegexp(regexp, s[, max_substrings]))
```
**Arguments**
- `regexp` — Regular expression. Constant. [String](../data-types/string.md) or [FixedString](../data-types/fixedstring.md).
- `s` — The string to split. [String](../../sql-reference/data-types/string.md).
- `max_substrings` — An optional `Int64` defaulting to 0. When `max_substrings` > 0, the returned substrings will be no more than `max_substrings`, otherwise the function will return as many substrings as possible.
**Returned value(s)**
@ -146,7 +151,7 @@ Result:
└────────────────────────────┘
```
## splitByWhitespace(s)
## splitByWhitespace(s[, max_substrings])
Splits a string into substrings separated by whitespace characters.
Returns an array of selected substrings.
@ -154,12 +159,14 @@ Returns an array of selected substrings.
**Syntax**
``` sql
splitByWhitespace(s)
splitByWhitespace(s[, max_substrings]))
```
**Arguments**
- `s` — The string to split. [String](../../sql-reference/data-types/string.md).
- `max_substrings` — An optional `Int64` defaulting to 0. When `max_substrings` > 0, the returned substrings will be no more than `max_substrings`, otherwise the function will return as many substrings as possible.
**Returned value(s)**
@ -179,7 +186,7 @@ SELECT splitByWhitespace(' 1! a, b. ');
└─────────────────────────────────────┘
```
## splitByNonAlpha(s)
## splitByNonAlpha(s[, max_substrings])
Splits a string into substrings separated by whitespace and punctuation characters.
Returns an array of selected substrings.
@ -187,12 +194,14 @@ Returns an array of selected substrings.
**Syntax**
``` sql
splitByNonAlpha(s)
splitByNonAlpha(s[, max_substrings]))
```
**Arguments**
- `s` — The string to split. [String](../../sql-reference/data-types/string.md).
- `max_substrings` — An optional `Int64` defaulting to 0. When `max_substrings` > 0, the returned substrings will be no more than `max_substrings`, otherwise the function will return as many substrings as possible.
**Returned value(s)**
@ -217,10 +226,28 @@ SELECT splitByNonAlpha(' 1! a, b. ');
Concatenates string representations of values listed in the array with the separator. `separator` is an optional parameter: a constant string, set to an empty string by default.
Returns the string.
## alphaTokens(s)
## alphaTokens(s[, max_substrings]), splitByAlpha(s[, max_substrings])
Selects substrings of consecutive bytes from the ranges a-z and A-Z.Returns an array of substrings.
**Syntax**
``` sql
alphaTokens(s[, max_substrings]))
splitByAlpha(s[, max_substrings])
```
**Arguments**
- `s` — The string to split. [String](../../sql-reference/data-types/string.md).
- `max_substrings` — An optional `Int64` defaulting to 0. When `max_substrings` > 0, the returned substrings will be no more than `max_substrings`, otherwise the function will return as many substrings as possible.
**Returned value(s)**
Returns an array of selected substrings.
Type: [Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md)).
**Example**
``` sql

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@ -131,7 +131,7 @@ Type: `UInt32`.
### regionToPopulation(id\[, geobase\])
Gets the population for a region.
The population can be recorded in files with the geobase. See the section “External dictionaries”.
The population can be recorded in files with the geobase. See the section “Dictionaries”.
If the population is not recorded for the region, it returns 0.
In the geobase, the population might be recorded for child regions, but not for parent regions.

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@ -35,11 +35,11 @@ These actions are described in detail below.
ADD COLUMN [IF NOT EXISTS] name [type] [default_expr] [codec] [AFTER name_after | FIRST]
```
Adds a new column to the table with the specified `name`, `type`, [`codec`](../create/table.md#codecs) and `default_expr` (see the section [Default expressions](../../../sql-reference/statements/create/table.md#create-default-values)).
Adds a new column to the table with the specified `name`, `type`, [`codec`](../create/table.md/#codecs) and `default_expr` (see the section [Default expressions](/docs/en/sql-reference/statements/create/table.md/#create-default-values)).
If the `IF NOT EXISTS` clause is included, the query won’t return an error if the column already exists. If you specify `AFTER name_after` (the name of another column), the column is added after the specified one in the list of table columns. If you want to add a column to the beginning of the table use the `FIRST` clause. Otherwise, the column is added to the end of the table. For a chain of actions, `name_after` can be the name of a column that is added in one of the previous actions.
Adding a column just changes the table structure, without performing any actions with data. The data does not appear on the disk after `ALTER`. If the data is missing for a column when reading from the table, it is filled in with default values (by performing the default expression if there is one, or using zeros or empty strings). The column appears on the disk after merging data parts (see [MergeTree](../../../engines/table-engines/mergetree-family/mergetree.md)).
Adding a column just changes the table structure, without performing any actions with data. The data does not appear on the disk after `ALTER`. If the data is missing for a column when reading from the table, it is filled in with default values (by performing the default expression if there is one, or using zeros or empty strings). The column appears on the disk after merging data parts (see [MergeTree](/docs/en/engines/table-engines/mergetree-family/mergetree.md)).
This approach allows us to complete the `ALTER` query instantly, without increasing the volume of old data.
@ -76,7 +76,7 @@ Deletes the column with the name `name`. If the `IF EXISTS` clause is specified,
Deletes data from the file system. Since this deletes entire files, the query is completed almost instantly.
:::warning
You can’t delete a column if it is referenced by [materialized view](../../../sql-reference/statements/create/view.md#materialized). Otherwise, it returns an error.
You can’t delete a column if it is referenced by [materialized view](/docs/en/sql-reference/statements/create/view.md/#materialized). Otherwise, it returns an error.
:::
Example:
@ -107,7 +107,7 @@ ALTER TABLE visits RENAME COLUMN webBrowser TO browser
CLEAR COLUMN [IF EXISTS] name IN PARTITION partition_name
```
Resets all data in a column for a specified partition. Read more about setting the partition name in the section [How to set the partition expression](partition.md#how-to-set-partition-expression).
Resets all data in a column for a specified partition. Read more about setting the partition name in the section [How to set the partition expression](partition.md/#how-to-set-partition-expression).
If the `IF EXISTS` clause is specified, the query won’t return an error if the column does not exist.
@ -127,7 +127,7 @@ Adds a comment to the column. If the `IF EXISTS` clause is specified, the query
Each column can have one comment. If a comment already exists for the column, a new comment overwrites the previous comment.
Comments are stored in the `comment_expression` column returned by the [DESCRIBE TABLE](../../../sql-reference/statements/describe-table.md) query.
Comments are stored in the `comment_expression` column returned by the [DESCRIBE TABLE](/docs/en/sql-reference/statements/describe-table.md) query.
Example:
@ -152,15 +152,15 @@ This query changes the `name` column properties:
- TTL
For examples of columns compression CODECS modifying, see [Column Compression Codecs](../create/table.md#codecs).
For examples of columns compression CODECS modifying, see [Column Compression Codecs](../create/table.md/#codecs).
For examples of columns TTL modifying, see [Column TTL](../../../engines/table-engines/mergetree-family/mergetree.md#mergetree-column-ttl).
For examples of columns TTL modifying, see [Column TTL](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#mergetree-column-ttl).
If the `IF EXISTS` clause is specified, the query won’t return an error if the column does not exist.
The query also can change the order of the columns using `FIRST | AFTER` clause, see [ADD COLUMN](#alter_add-column) description.
When changing the type, values are converted as if the [toType](../../../sql-reference/functions/type-conversion-functions.md) functions were applied to them. If only the default expression is changed, the query does not do anything complex, and is completed almost instantly.
When changing the type, values are converted as if the [toType](/docs/en/sql-reference/functions/type-conversion-functions.md) functions were applied to them. If only the default expression is changed, the query does not do anything complex, and is completed almost instantly.
Example:
@ -246,7 +246,7 @@ SELECT groupArray(x), groupArray(s) FROM tmp;
**See Also**
- [MATERIALIZED](../../statements/create/table.md#materialized).
- [MATERIALIZED](/docs/en/sql-reference/statements/create/table.md/#materialized).
## Limitations
@ -254,8 +254,8 @@ The `ALTER` query lets you create and delete separate elements (columns) in nest
There is no support for deleting columns in the primary key or the sampling key (columns that are used in the `ENGINE` expression). Changing the type for columns that are included in the primary key is only possible if this change does not cause the data to be modified (for example, you are allowed to add values to an Enum or to change a type from `DateTime` to `UInt32`).
If the `ALTER` query is not sufficient to make the table changes you need, you can create a new table, copy the data to it using the [INSERT SELECT](../../../sql-reference/statements/insert-into.md#insert_query_insert-select) query, then switch the tables using the [RENAME](../../../sql-reference/statements/rename.md#rename-table) query and delete the old table. You can use the [clickhouse-copier](../../../operations/utilities/clickhouse-copier.md) as an alternative to the `INSERT SELECT` query.
If the `ALTER` query is not sufficient to make the table changes you need, you can create a new table, copy the data to it using the [INSERT SELECT](/docs/en/sql-reference/statements/insert-into.md/#insert_query_insert-select) query, then switch the tables using the [RENAME](/docs/en/sql-reference/statements/rename.md/#rename-table) query and delete the old table. You can use the [clickhouse-copier](/docs/en/operations/utilities/clickhouse-copier.md) as an alternative to the `INSERT SELECT` query.
The `ALTER` query blocks all reads and writes for the table. In other words, if a long `SELECT` is running at the time of the `ALTER` query, the `ALTER` query will wait for it to complete. At the same time, all new queries to the same table will wait while this `ALTER` is running.
For tables that do not store data themselves (such as [Merge](../../../sql-reference/statements/alter/index.md) and [Distributed](../../../sql-reference/statements/alter/index.md)), `ALTER` just changes the table structure, and does not change the structure of subordinate tables. For example, when running ALTER for a `Distributed` table, you will also need to run `ALTER` for the tables on all remote servers.
For tables that do not store data themselves (such as [Merge](/docs/en/sql-reference/statements/alter/index.md) and [Distributed](/docs/en/sql-reference/statements/alter/index.md)), `ALTER` just changes the table structure, and does not change the structure of subordinate tables. For example, when running ALTER for a `Distributed` table, you will also need to run `ALTER` for the tables on all remote servers.

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@ -10,21 +10,21 @@ sidebar_label: DELETE
ALTER TABLE [db.]table [ON CLUSTER cluster] DELETE WHERE filter_expr
```
Deletes data matching the specified filtering expression. Implemented as a [mutation](../../../sql-reference/statements/alter/index.md#mutations).
Deletes data matching the specified filtering expression. Implemented as a [mutation](/docs/en/sql-reference/statements/alter/index.md/#mutations).
:::note
The `ALTER TABLE` prefix makes this syntax different from most other systems supporting SQL. It is intended to signify that unlike similar queries in OLTP databases this is a heavy operation not designed for frequent use. `ALTER TABLE` is considered a heavyweight operation that requires the underlying data to be merged before it is deleted. For MergeTree tables, consider using the [`DELETE FROM` query](../delete.md), which performs a lightweight delete and can be considerably faster.
The `ALTER TABLE` prefix makes this syntax different from most other systems supporting SQL. It is intended to signify that unlike similar queries in OLTP databases this is a heavy operation not designed for frequent use. `ALTER TABLE` is considered a heavyweight operation that requires the underlying data to be merged before it is deleted. For MergeTree tables, consider using the [`DELETE FROM` query](/docs/en/sql-reference/statements/delete.md), which performs a lightweight delete and can be considerably faster.
:::
The `filter_expr` must be of type `UInt8`. The query deletes rows in the table for which this expression takes a non-zero value.
One query can contain several commands separated by commas.
The synchronicity of the query processing is defined by the [mutations_sync](../../../operations/settings/settings.md#mutations_sync) setting. By default, it is asynchronous.
The synchronicity of the query processing is defined by the [mutations_sync](/docs/en/operations/settings/settings.md/#mutations_sync) setting. By default, it is asynchronous.
**See also**
- [Mutations](../../../sql-reference/statements/alter/index.md#mutations)
- [Synchronicity of ALTER Queries](../../../sql-reference/statements/alter/index.md#synchronicity-of-alter-queries)
- [mutations_sync](../../../operations/settings/settings.md#mutations_sync) setting
- [Mutations](/docs/en/sql-reference/statements/alter/index.md/#mutations)
- [Synchronicity of ALTER Queries](/docs/en/sql-reference/statements/alter/index.md/#synchronicity-of-alter-queries)
- [mutations_sync](/docs/en/operations/settings/settings.md/#mutations_sync) setting

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@ -8,43 +8,43 @@ sidebar_label: ALTER
Most `ALTER TABLE` queries modify table settings or data:
- [COLUMN](../../../sql-reference/statements/alter/column.md)
- [PARTITION](../../../sql-reference/statements/alter/partition.md)
- [DELETE](../../../sql-reference/statements/alter/delete.md)
- [UPDATE](../../../sql-reference/statements/alter/update.md)
- [ORDER BY](../../../sql-reference/statements/alter/order-by.md)
- [INDEX](../../../sql-reference/statements/alter/index/index.md)
- [CONSTRAINT](../../../sql-reference/statements/alter/constraint.md)
- [TTL](../../../sql-reference/statements/alter/ttl.md)
- [COLUMN](/docs/en/sql-reference/statements/alter/column.md)
- [PARTITION](/docs/en/sql-reference/statements/alter/partition.md)
- [DELETE](/docs/en/sql-reference/statements/alter/delete.md)
- [UPDATE](/docs/en/sql-reference/statements/alter/update.md)
- [ORDER BY](/docs/en/sql-reference/statements/alter/order-by.md)
- [INDEX](/docs/en/sql-reference/statements/alter/skipping-index.md)
- [CONSTRAINT](/docs/en/sql-reference/statements/alter/constraint.md)
- [TTL](/docs/en/sql-reference/statements/alter/ttl.md)
:::note
Most `ALTER TABLE` queries are supported only for [\*MergeTree](../../../engines/table-engines/mergetree-family/index.md) tables, as well as [Merge](../../../engines/table-engines/special/merge.md) and [Distributed](../../../engines/table-engines/special/distributed.md).
Most `ALTER TABLE` queries are supported only for [\*MergeTree](/docs/en/engines/table-engines/mergetree-family/index.md) tables, as well as [Merge](/docs/en/engines/table-engines/special/merge.md) and [Distributed](/docs/en/engines/table-engines/special/distributed.md).
:::
These `ALTER` statements manipulate views:
- [ALTER TABLE ... MODIFY QUERY](../../../sql-reference/statements/alter/view.md) — Modifies a [Materialized view](../create/view.md#materialized) structure.
- [ALTER LIVE VIEW](../../../sql-reference/statements/alter/view.md#alter-live-view) — Refreshes a [Live view](../create/view.md#live-view).
- [ALTER TABLE ... MODIFY QUERY](/docs/en/sql-reference/statements/alter/view.md) — Modifies a [Materialized view](/docs/en/sql-reference/statements/create/view.md/#materialized) structure.
- [ALTER LIVE VIEW](/docs/en/sql-reference/statements/alter/view.md/#alter-live-view) — Refreshes a [Live view](/docs/en/sql-reference/statements/create/view.md/#live-view).
These `ALTER` statements modify entities related to role-based access control:
- [USER](../../../sql-reference/statements/alter/user.md)
- [ROLE](../../../sql-reference/statements/alter/role.md)
- [QUOTA](../../../sql-reference/statements/alter/quota.md)
- [ROW POLICY](../../../sql-reference/statements/alter/row-policy.md)
- [SETTINGS PROFILE](../../../sql-reference/statements/alter/settings-profile.md)
- [USER](/docs/en/sql-reference/statements/alter/user.md)
- [ROLE](/docs/en/sql-reference/statements/alter/role.md)
- [QUOTA](/docs/en/sql-reference/statements/alter/quota.md)
- [ROW POLICY](/docs/en/sql-reference/statements/alter/row-policy.md)
- [SETTINGS PROFILE](/docs/en/sql-reference/statements/alter/settings-profile.md)
[ALTER TABLE ... MODIFY COMMENT](../../../sql-reference/statements/alter/comment.md) statement adds, modifies, or removes comments to the table, regardless if it was set before or not.
[ALTER TABLE ... MODIFY COMMENT](/docs/en/sql-reference/statements/alter/comment.md) statement adds, modifies, or removes comments to the table, regardless if it was set before or not.
## Mutations
`ALTER` queries that are intended to manipulate table data are implemented with a mechanism called “mutations”, most notably [ALTER TABLE … DELETE](../../../sql-reference/statements/alter/delete.md) and [ALTER TABLE … UPDATE](../../../sql-reference/statements/alter/update.md). They are asynchronous background processes similar to merges in [MergeTree](../../../engines/table-engines/mergetree-family/index.md) tables that to produce new “mutated” versions of parts.
`ALTER` queries that are intended to manipulate table data are implemented with a mechanism called “mutations”, most notably [ALTER TABLE … DELETE](/docs/en/sql-reference/statements/alter/delete.md) and [ALTER TABLE … UPDATE](/docs/en/sql-reference/statements/alter/update.md). They are asynchronous background processes similar to merges in [MergeTree](/docs/en/engines/table-engines/mergetree-family/index.md) tables that to produce new “mutated” versions of parts.
For `*MergeTree` tables mutations execute by **rewriting whole data parts**. There is no atomicity - parts are substituted for mutated parts as soon as they are ready and a `SELECT` query that started executing during a mutation will see data from parts that have already been mutated along with data from parts that have not been mutated yet.
Mutations are totally ordered by their creation order and are applied to each part in that order. Mutations are also partially ordered with `INSERT INTO` queries: data that was inserted into the table before the mutation was submitted will be mutated and data that was inserted after that will not be mutated. Note that mutations do not block inserts in any way.
A mutation query returns immediately after the mutation entry is added (in case of replicated tables to ZooKeeper, for non-replicated tables - to the filesystem). The mutation itself executes asynchronously using the system profile settings. To track the progress of mutations you can use the [`system.mutations`](../../../operations/system-tables/mutations.md#system_tables-mutations) table. A mutation that was successfully submitted will continue to execute even if ClickHouse servers are restarted. There is no way to roll back the mutation once it is submitted, but if the mutation is stuck for some reason it can be cancelled with the [`KILL MUTATION`](../../../sql-reference/statements/kill.md#kill-mutation) query.
A mutation query returns immediately after the mutation entry is added (in case of replicated tables to ZooKeeper, for non-replicated tables - to the filesystem). The mutation itself executes asynchronously using the system profile settings. To track the progress of mutations you can use the [`system.mutations`](/docs/en/operations/system-tables/mutations.md/#system_tables-mutations) table. A mutation that was successfully submitted will continue to execute even if ClickHouse servers are restarted. There is no way to roll back the mutation once it is submitted, but if the mutation is stuck for some reason it can be cancelled with the [`KILL MUTATION`](/docs/en/sql-reference/statements/kill.md/#kill-mutation) query.
Entries for finished mutations are not deleted right away (the number of preserved entries is determined by the `finished_mutations_to_keep` storage engine parameter). Older mutation entries are deleted.
@ -52,12 +52,12 @@ Entries for finished mutations are not deleted right away (the number of preserv
For non-replicated tables, all `ALTER` queries are performed synchronously. For replicated tables, the query just adds instructions for the appropriate actions to `ZooKeeper`, and the actions themselves are performed as soon as possible. However, the query can wait for these actions to be completed on all the replicas.
For all `ALTER` queries, you can use the [replication_alter_partitions_sync](../../../operations/settings/settings.md#replication-alter-partitions-sync) setting to set up waiting.
For all `ALTER` queries, you can use the [replication_alter_partitions_sync](/docs/en/operations/settings/settings.md/#replication-alter-partitions-sync) setting to set up waiting.
You can specify how long (in seconds) to wait for inactive replicas to execute all `ALTER` queries with the [replication_wait_for_inactive_replica_timeout](../../../operations/settings/settings.md#replication-wait-for-inactive-replica-timeout) setting.
You can specify how long (in seconds) to wait for inactive replicas to execute all `ALTER` queries with the [replication_wait_for_inactive_replica_timeout](/docs/en/operations/settings/settings.md/#replication-wait-for-inactive-replica-timeout) setting.
:::note
For all `ALTER` queries, if `replication_alter_partitions_sync = 2` and some replicas are not active for more than the time, specified in the `replication_wait_for_inactive_replica_timeout` setting, then an exception `UNFINISHED` is thrown.
:::
For `ALTER TABLE ... UPDATE|DELETE` queries the synchronicity is defined by the [mutations_sync](../../../operations/settings/settings.md#mutations_sync) setting.
For `ALTER TABLE ... UPDATE|DELETE` queries the synchronicity is defined by the [mutations_sync](/docs/en/operations/settings/settings.md/#mutations_sync) setting.

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@ -5,7 +5,7 @@ sidebar_label: PARTITION
title: "Manipulating Partitions and Parts"
---
The following operations with [partitions](../../../engines/table-engines/mergetree-family/custom-partitioning-key.md) are available:
The following operations with [partitions](/docs/en/engines/table-engines/mergetree-family/custom-partitioning-key.md) are available:
- [DETACH PARTITION\|PART](#detach-partitionpart) — Moves a partition or part to the `detached` directory and forget it.
- [DROP PARTITION\|PART](#drop-partitionpart) — Deletes a partition or part.
@ -43,7 +43,7 @@ Read about setting the partition expression in a section [How to set the partiti
After the query is executed, you can do whatever you want with the data in the `detached` directory — delete it from the file system, or just leave it.
This query is replicated – it moves the data to the `detached` directory on all replicas. Note that you can execute this query only on a leader replica. To find out if a replica is a leader, perform the `SELECT` query to the [system.replicas](../../../operations/system-tables/replicas.md#system_tables-replicas) table. Alternatively, it is easier to make a `DETACH` query on all replicas - all the replicas throw an exception, except the leader replicas (as multiple leaders are allowed).
This query is replicated – it moves the data to the `detached` directory on all replicas. Note that you can execute this query only on a leader replica. To find out if a replica is a leader, perform the `SELECT` query to the [system.replicas](/docs/en/operations/system-tables/replicas.md/#system_tables-replicas) table. Alternatively, it is easier to make a `DETACH` query on all replicas - all the replicas throw an exception, except the leader replicas (as multiple leaders are allowed).
## DROP PARTITION\|PART
@ -175,7 +175,7 @@ At the time of execution, for a data snapshot, the query creates hardlinks to a
- if the `WITH NAME` parameter is specified, then the value of the `'backup_name'` parameter is used instead of the incremental number.
:::note
If you use [a set of disks for data storage in a table](../../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-multiple-volumes), the `shadow/N` directory appears on every disk, storing data parts that matched by the `PARTITION` expression.
If you use [a set of disks for data storage in a table](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-multiple-volumes), the `shadow/N` directory appears on every disk, storing data parts that matched by the `PARTITION` expression.
:::
The same structure of directories is created inside the backup as inside `/var/lib/clickhouse/`. The query performs `chmod` for all files, forbidding writing into them.
@ -249,7 +249,7 @@ Although the query is called `ALTER TABLE`, it does not change the table structu
## MOVE PARTITION\|PART
Moves partitions or data parts to another volume or disk for `MergeTree`-engine tables. See [Using Multiple Block Devices for Data Storage](../../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-multiple-volumes).
Moves partitions or data parts to another volume or disk for `MergeTree`-engine tables. See [Using Multiple Block Devices for Data Storage](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#table_engine-mergetree-multiple-volumes).
``` sql
ALTER TABLE table_name [ON CLUSTER cluster] MOVE PARTITION|PART partition_expr TO DISK|VOLUME 'disk_name'
@ -270,7 +270,7 @@ ALTER TABLE hits MOVE PARTITION '2019-09-01' TO DISK 'fast_ssd'
## UPDATE IN PARTITION
Manipulates data in the specifies partition matching the specified filtering expression. Implemented as a [mutation](../../../sql-reference/statements/alter/index.md#mutations).
Manipulates data in the specifies partition matching the specified filtering expression. Implemented as a [mutation](/docs/en/sql-reference/statements/alter/index.md/#mutations).
Syntax:
@ -286,11 +286,11 @@ ALTER TABLE mt UPDATE x = x + 1 IN PARTITION 2 WHERE p = 2;
### See Also
- [UPDATE](../../../sql-reference/statements/alter/update.md#alter-table-update-statements)
- [UPDATE](/docs/en/sql-reference/statements/alter/update.md/#alter-table-update-statements)
## DELETE IN PARTITION
Deletes data in the specifies partition matching the specified filtering expression. Implemented as a [mutation](../../../sql-reference/statements/alter/index.md#mutations).
Deletes data in the specifies partition matching the specified filtering expression. Implemented as a [mutation](/docs/en/sql-reference/statements/alter/index.md/#mutations).
Syntax:
@ -306,7 +306,7 @@ ALTER TABLE mt DELETE IN PARTITION 2 WHERE p = 2;
### See Also
- [DELETE](../../../sql-reference/statements/alter/delete.md#alter-mutations)
- [DELETE](/docs/en/sql-reference/statements/alter/delete.md/#alter-mutations)
## How to Set Partition Expression
@ -315,16 +315,16 @@ You can specify the partition expression in `ALTER ... PARTITION` queries in dif
- As a value from the `partition` column of the `system.parts` table. For example, `ALTER TABLE visits DETACH PARTITION 201901`.
- As a tuple of expressions or constants that matches (in types) the table partitioning keys tuple. In the case of a single element partitioning key, the expression should be wrapped in the `tuple (...)` function. For example, `ALTER TABLE visits DETACH PARTITION tuple(toYYYYMM(toDate('2019-01-25')))`.
- Using the partition ID. Partition ID is a string identifier of the partition (human-readable, if possible) that is used as the names of partitions in the file system and in ZooKeeper. The partition ID must be specified in the `PARTITION ID` clause, in a single quotes. For example, `ALTER TABLE visits DETACH PARTITION ID '201901'`.
- In the [ALTER ATTACH PART](#alter_attach-partition) and [DROP DETACHED PART](#alter_drop-detached) query, to specify the name of a part, use string literal with a value from the `name` column of the [system.detached_parts](../../../operations/system-tables/detached_parts.md#system_tables-detached_parts) table. For example, `ALTER TABLE visits ATTACH PART '201901_1_1_0'`.
- In the [ALTER ATTACH PART](#alter_attach-partition) and [DROP DETACHED PART](#alter_drop-detached) query, to specify the name of a part, use string literal with a value from the `name` column of the [system.detached_parts](/docs/en/operations/system-tables/detached_parts.md/#system_tables-detached_parts) table. For example, `ALTER TABLE visits ATTACH PART '201901_1_1_0'`.
Usage of quotes when specifying the partition depends on the type of partition expression. For example, for the `String` type, you have to specify its name in quotes (`'`). For the `Date` and `Int*` types no quotes are needed.
All the rules above are also true for the [OPTIMIZE](../../../sql-reference/statements/optimize.md) query. If you need to specify the only partition when optimizing a non-partitioned table, set the expression `PARTITION tuple()`. For example:
All the rules above are also true for the [OPTIMIZE](/docs/en/sql-reference/statements/optimize.md) query. If you need to specify the only partition when optimizing a non-partitioned table, set the expression `PARTITION tuple()`. For example:
``` sql
OPTIMIZE TABLE table_not_partitioned PARTITION tuple() FINAL;
```
`IN PARTITION` specifies the partition to which the [UPDATE](../../../sql-reference/statements/alter/update.md#alter-table-update-statements) or [DELETE](../../../sql-reference/statements/alter/delete.md#alter-mutations) expressions are applied as a result of the `ALTER TABLE` query. New parts are created only from the specified partition. In this way, `IN PARTITION` helps to reduce the load when the table is divided into many partitions, and you only need to update the data point-by-point.
`IN PARTITION` specifies the partition to which the [UPDATE](/docs/en/sql-reference/statements/alter/update.md/#alter-table-update-statements) or [DELETE](/docs/en/sql-reference/statements/alter/delete.md/#alter-mutations) expressions are applied as a result of the `ALTER TABLE` query. New parts are created only from the specified partition. In this way, `IN PARTITION` helps to reduce the load when the table is divided into many partitions, and you only need to update the data point-by-point.
The examples of `ALTER ... PARTITION` queries are demonstrated in the tests [`00502_custom_partitioning_local`](https://github.com/ClickHouse/ClickHouse/blob/master/tests/queries/0_stateless/00502_custom_partitioning_local.sql) and [`00502_custom_partitioning_replicated_zookeeper`](https://github.com/ClickHouse/ClickHouse/blob/master/tests/queries/0_stateless/00502_custom_partitioning_replicated_zookeeper.sql).

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@ -2,10 +2,135 @@
slug: /en/sql-reference/statements/alter/projection
sidebar_position: 49
sidebar_label: PROJECTION
title: "Manipulating Projections"
title: "Projections"
---
The following operations with [projections](../../../engines/table-engines/mergetree-family/mergetree.md#projections) are available:
Projections store data in a format that optimizes query execution, this feature is useful for:
- Running queries on a column that is not a part of the primary key
- Pre-aggregating columns, it will reduce both computation and IO
You can define one or more projections for a table, and during the query analysis the projection with the least data to scan will be selected by ClickHouse without modifying the query provided by the user.
## Example filtering without using primary keys
Creating the table:
```
CREATE TABLE visits_order
(
`user_id` UInt64,
`user_name` String,
`pages_visited` Nullable(Float64),
`user_agent` String
)
ENGINE = MergeTree()
PRIMARY KEY user_agent
```
Using `ALTER TABLE`, we could add the Projection to an existing table:
```
ALTER TABLE visits_order ADD PROJECTION user_name_projection (
SELECT
*
ORDER BY user_name
)
ALTER TABLE visits_order MATERIALIZE PROJECTION user_name_projection
```
Inserting the data:
```
INSERT INTO visits_order SELECT
number,
'test',
1.5 * (number / 2),
'Android'
FROM numbers(1, 100);
```
The Projection will allow us to filter by `user_name` fast even if in the original Table `user_name` was not defined as a `PRIMARY_KEY`.
At query time ClickHouse determined that less data will be processed if the projection is used, as the data is ordered by `user_name`.
```
SELECT
*
FROM visits_order
WHERE user_name='test'
LIMIT 2
```
To verify that a query is using the projection, we could review the `system.query_log` table. On the `projections` field we have the name of the projection used or empty if none has been used:
```
SELECT query, projections FROM system.query_log WHERE query_id='<query_id>'
```
## Example pre-aggregation query
Creating the table with the Projection:
```
CREATE TABLE visits
(
`user_id` UInt64,
`user_name` String,
`pages_visited` Nullable(Float64),
`user_agent` String,
PROJECTION projection_visits_by_user
(
SELECT
user_agent,
sum(pages_visited)
GROUP BY user_id, user_agent
)
)
ENGINE = MergeTree()
ORDER BY user_agent
```
Inserting the data:
```
INSERT INTO visits SELECT
number,
'test',
1.5 * (number / 2),
'Android'
FROM numbers(1, 100);
```
```
INSERT INTO visits SELECT
number,
'test',
1. * (number / 2),
'IOS'
FROM numbers(100, 500);
```
We will execute a first query using `GROUP BY` using the field `user_agent`, this query will not use the projection defined as the pre-aggregation does not match.
```
SELECT
user_agent,
count(DISTINCT user_id)
FROM visits
GROUP BY user_agent
```
To use the projection we could execute queries that select part of, or all of the pre-aggregation and `GROUP BY` fields.
```
SELECT
user_agent
FROM visits
WHERE user_id > 50 AND user_id < 150
GROUP BY user_agent
```
```
SELECT
user_agent,
sum(pages_visited)
FROM visits
GROUP BY user_id
```
As mentioned before, we could review the `system.query_log` table. On the `projections` field we have the name of the projection used or empty if none has been used:
```
SELECT query, projections FROM system.query_log WHERE query_id='<query_id>'
```
# Manipulating Projections
The following operations with [projections](/docs/en/engines/table-engines/mergetree-family/mergetree.md/#projections) are available:
## ADD PROJECTION
@ -13,15 +138,15 @@ The following operations with [projections](../../../engines/table-engines/merge
## DROP PROJECTION
`ALTER TABLE [db].name DROP PROJECTION name` - Removes projection description from tables metadata and deletes projection files from disk. Implemented as a [mutation](../../../sql-reference/statements/alter/index.md#mutations).
`ALTER TABLE [db].name DROP PROJECTION name` - Removes projection description from tables metadata and deletes projection files from disk. Implemented as a [mutation](/docs/en/sql-reference/statements/alter/index.md/#mutations).
## MATERIALIZE PROJECTION
`ALTER TABLE [db.]table MATERIALIZE PROJECTION name IN PARTITION partition_name` - The query rebuilds the projection `name` in the partition `partition_name`. Implemented as a [mutation](../../../sql-reference/statements/alter/index.md#mutations).
`ALTER TABLE [db.]table MATERIALIZE PROJECTION name IN PARTITION partition_name` - The query rebuilds the projection `name` in the partition `partition_name`. Implemented as a [mutation](/docs/en/sql-reference/statements/alter/index.md/#mutations).
## CLEAR PROJECTION
`ALTER TABLE [db.]table CLEAR PROJECTION name IN PARTITION partition_name` - Deletes projection files from disk without removing description. Implemented as a [mutation](../../../sql-reference/statements/alter/index.md#mutations).
`ALTER TABLE [db.]table CLEAR PROJECTION name IN PARTITION partition_name` - Deletes projection files from disk without removing description. Implemented as a [mutation](/docs/en/sql-reference/statements/alter/index.md/#mutations).
The commands `ADD`, `DROP` and `CLEAR` are lightweight in a sense that they only change metadata or remove files.
@ -29,5 +154,5 @@ The commands `ADD`, `DROP` and `CLEAR` are lightweight in a sense that they only
Also, they are replicated, syncing projections metadata via ClickHouse Keeper or ZooKeeper.
:::note
Projection manipulation is supported only for tables with [`*MergeTree`](../../../engines/table-engines/mergetree-family/mergetree.md) engine (including [replicated](../../../engines/table-engines/mergetree-family/replication.md) variants).
Projection manipulation is supported only for tables with [`*MergeTree`](/docs/en/engines/table-engines/mergetree-family/mergetree.md) engine (including [replicated](/docs/en/engines/table-engines/mergetree-family/replication.md) variants).
:::

7
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@ -1,5 +1,6 @@
---
slug: /en/sql-reference/statements/alter/index
slug: /en/sql-reference/statements/alter/skipping-index
toc_hidden_folder: true
sidebar_position: 42
sidebar_label: INDEX
@ -13,12 +14,12 @@ The following operations are available:
- `ALTER TABLE [db].table_name [ON CLUSTER cluster] DROP INDEX name` - Removes index description from tables metadata and deletes index files from disk.
- `ALTER TABLE [db.]table_name [ON CLUSTER cluster] MATERIALIZE INDEX name [IN PARTITION partition_name]` - Rebuilds the secondary index `name` for the specified `partition_name`. Implemented as a [mutation](../../../../sql-reference/statements/alter/index.md#mutations). If `IN PARTITION` part is omitted then it rebuilds the index for the whole table data.
- `ALTER TABLE [db.]table_name [ON CLUSTER cluster] MATERIALIZE INDEX name [IN PARTITION partition_name]` - Rebuilds the secondary index `name` for the specified `partition_name`. Implemented as a [mutation](/docs/en/sql-reference/statements/alter/index.md/#mutations). If `IN PARTITION` part is omitted then it rebuilds the index for the whole table data.
The first two commands are lightweight in a sense that they only change metadata or remove files.
Also, they are replicated, syncing indices metadata via ZooKeeper.
:::note
Index manipulation is supported only for tables with [`*MergeTree`](../../../../engines/table-engines/mergetree-family/mergetree.md) engine (including [replicated](../../../../engines/table-engines/mergetree-family/replication.md) variants).
Index manipulation is supported only for tables with [`*MergeTree`](/docs/en/engines/table-engines/mergetree-family/mergetree.md) engine (including [replicated](/docs/en/engines/table-engines/mergetree-family/replication.md) variants).
:::

10
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@ -10,7 +10,7 @@ sidebar_label: UPDATE
ALTER TABLE [db.]table [ON CLUSTER cluster] UPDATE column1 = expr1 [, ...] WHERE filter_expr
```
Manipulates data matching the specified filtering expression. Implemented as a [mutation](../../../sql-reference/statements/alter/index.md#mutations).
Manipulates data matching the specified filtering expression. Implemented as a [mutation](/docs/en/sql-reference/statements/alter/index.md/#mutations).
:::note
The `ALTER TABLE` prefix makes this syntax different from most other systems supporting SQL. It is intended to signify that unlike similar queries in OLTP databases this is a heavy operation not designed for frequent use.
@ -20,11 +20,11 @@ The `filter_expr` must be of type `UInt8`. This query updates values of specifie
One query can contain several commands separated by commas.
The synchronicity of the query processing is defined by the [mutations_sync](../../../operations/settings/settings.md#mutations_sync) setting. By default, it is asynchronous.
The synchronicity of the query processing is defined by the [mutations_sync](/docs/en/operations/settings/settings.md/#mutations_sync) setting. By default, it is asynchronous.
**See also**
- [Mutations](../../../sql-reference/statements/alter/index.md#mutations)
- [Synchronicity of ALTER Queries](../../../sql-reference/statements/alter/index.md#synchronicity-of-alter-queries)
- [mutations_sync](../../../operations/settings/settings.md#mutations_sync) setting
- [Mutations](/docs/en/sql-reference/statements/alter/index.md/#mutations)
- [Synchronicity of ALTER Queries](/docs/en/sql-reference/statements/alter/index.md/#synchronicity-of-alter-queries)
- [mutations_sync](/docs/en/operations/settings/settings.md/#mutations_sync) setting

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@ -5,9 +5,9 @@ sidebar_label: DICTIONARY
title: "CREATE DICTIONARY"
---
Creates a new [external dictionary](../../../sql-reference/dictionaries/external-dictionaries/external-dicts.md) with given [structure](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md), [source](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md), [layout](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-layout.md) and [lifetime](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-lifetime.md).
Creates a new [dictionary](../../../sql-reference/dictionaries/external-dictionaries/external-dicts.md) with given [structure](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md), [source](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md), [layout](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-layout.md) and [lifetime](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-lifetime.md).
**Syntax**
## Syntax
``` sql
CREATE [OR REPLACE] DICTIONARY [IF NOT EXISTS] [db.]dictionary_name [ON CLUSTER cluster]
@ -25,17 +25,21 @@ SETTINGS(setting_name = setting_value, setting_name = setting_value, ...)
COMMENT 'Comment'
```
External dictionary structure consists of attributes. Dictionary attributes are specified similarly to table columns. The only required attribute property is its type, all other properties may have default values.
The dictionary structure consists of attributes. Dictionary attributes are specified similarly to table columns. The only required attribute property is its type, all other properties may have default values.
`ON CLUSTER` clause allows creating dictionary on a cluster, see [Distributed DDL](../../../sql-reference/distributed-ddl.md).
Depending on dictionary [layout](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-layout.md) one or more attributes can be specified as dictionary keys.
For more information, see [External Dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts.md) section.
## SOURCE
You can add a comment to the dictionary when you creating it using `COMMENT` clause.
The source for a dictionary can be a:
- table in the current ClickHouse service
- table in a remote ClickHouse service
- file available by HTTP(S)
- another database
**Example**
### Create a dictionary from a table in the current ClickHouse service
Input table `source_table`:
@ -49,51 +53,81 @@ Input table `source_table`:
Creating the dictionary:
``` sql
CREATE DICTIONARY dictionary_with_comment
CREATE DICTIONARY id_value_dictionary
(
id UInt64,
value String
)
PRIMARY KEY id
SOURCE(CLICKHOUSE(HOST 'localhost' PORT tcpPort() TABLE 'source_table'))
SOURCE(CLICKHOUSE(TABLE 'source_table'))
LAYOUT(FLAT())
LIFETIME(MIN 0 MAX 1000)
COMMENT 'The temporary dictionary';
```
Output the dictionary:
``` sql
SHOW CREATE DICTIONARY dictionary_with_comment;
SHOW CREATE DICTIONARY id_value_dictionary;
```
```text
┌─statement───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ CREATE DICTIONARY default.dictionary_with_comment
```response
CREATE DICTIONARY default.id_value_dictionary
(
`id` UInt64,
`value` String
)
PRIMARY KEY id
SOURCE(CLICKHOUSE(HOST 'localhost' PORT tcpPort() TABLE 'source_table'))
SOURCE(CLICKHOUSE(TABLE 'source_table'))
LIFETIME(MIN 0 MAX 1000)
LAYOUT(FLAT())
COMMENT 'The temporary dictionary' │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
```
Output the comment to dictionary:
### Create a dictionary from a table in a remote ClickHouse service
``` sql
SELECT comment FROM system.dictionaries WHERE name == 'dictionary_with_comment' AND database == currentDatabase();
```
Input table (in the remote ClickHouse service) `source_table`:
``` text
┌─comment──────────────────┐
│ The temporary dictionary │
└──────────────────────────┘
┌─id─┬─value──┐
│ 1 │ First │
│ 2 │ Second │
└────┴────────┘
```
Creating the dictionary:
``` sql
CREATE DICTIONARY id_value_dictionary
(
id UInt64,
value String
)
PRIMARY KEY id
SOURCE(CLICKHOUSE(HOST 'HOSTNAME' PORT 9000 USER 'default' PASSWORD 'PASSWORD' TABLE 'source_table' DB 'default'))
LAYOUT(FLAT())
LIFETIME(MIN 0 MAX 1000)
```
### Create a dictionary from a file available by HTTP(S)
```sql
statement: CREATE DICTIONARY default.taxi_zone_dictionary
(
`LocationID` UInt16 DEFAULT 0,
`Borough` String,
`Zone` String,
`service_zone` String
)
PRIMARY KEY LocationID
SOURCE(HTTP(URL 'https://datasets-documentation.s3.eu-west-3.amazonaws.com/nyc-taxi/taxi_zone_lookup.csv' FORMAT 'CSVWithNames'))
LIFETIME(MIN 0 MAX 0)
LAYOUT(HASHED())
```
### Create a dictionary from another database
Please see the details in [Dictionary sources](/docs/en/sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md/#dbms).
**See Also**
- [system.dictionaries](../../../operations/system-tables/dictionaries.md) — This table contains information about [external dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts.md).
- For more information, see the [Dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts.md) section.
- [system.dictionaries](../../../operations/system-tables/dictionaries.md) — This table contains information about [Dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts.md).

44
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@ -8,25 +8,25 @@ sidebar_label: Statements
Statements represent various kinds of action you can perform using SQL queries. Each kind of statement has it’s own syntax and usage details that are described separately:
- [SELECT](../../sql-reference/statements/select/index.md)
- [INSERT INTO](../../sql-reference/statements/insert-into.md)
- [CREATE](../../sql-reference/statements/create/index.md)
- [ALTER](../../sql-reference/statements/alter/index.md)
- [SYSTEM](../../sql-reference/statements/system.md)
- [SHOW](../../sql-reference/statements/show.md)
- [GRANT](../../sql-reference/statements/grant.md)
- [REVOKE](../../sql-reference/statements/revoke.md)
- [ATTACH](../../sql-reference/statements/attach.md)
- [CHECK TABLE](../../sql-reference/statements/check-table.md)
- [DESCRIBE TABLE](../../sql-reference/statements/describe-table.md)
- [DETACH](../../sql-reference/statements/detach.md)
- [DROP](../../sql-reference/statements/drop.md)
- [EXISTS](../../sql-reference/statements/exists.md)
- [KILL](../../sql-reference/statements/kill.md)
- [OPTIMIZE](../../sql-reference/statements/optimize.md)
- [RENAME](../../sql-reference/statements/rename.md)
- [SET](../../sql-reference/statements/set.md)
- [SET ROLE](../../sql-reference/statements/set-role.md)
- [TRUNCATE](../../sql-reference/statements/truncate.md)
- [USE](../../sql-reference/statements/use.md)
- [EXPLAIN](../../sql-reference/statements/explain.md)
- [SELECT](/docs/en/sql-reference/statements/select/index.md)
- [INSERT INTO](/docs/en/sql-reference/statements/insert-into.md)
- [CREATE](/docs/en/sql-reference/statements/create/index.md)
- [ALTER](/docs/en/sql-reference/statements/alter/index.md)
- [SYSTEM](/docs/en/sql-reference/statements/system.md)
- [SHOW](/docs/en/sql-reference/statements/show.md)
- [GRANT](/docs/en/sql-reference/statements/grant.md)
- [REVOKE](/docs/en/sql-reference/statements/revoke.md)
- [ATTACH](/docs/en/sql-reference/statements/attach.md)
- [CHECK TABLE](/docs/en/sql-reference/statements/check-table.md)
- [DESCRIBE TABLE](/docs/en/sql-reference/statements/describe-table.md)
- [DETACH](/docs/en/sql-reference/statements/detach.md)
- [DROP](/docs/en/sql-reference/statements/drop.md)
- [EXISTS](/docs/en/sql-reference/statements/exists.md)
- [KILL](/docs/en/sql-reference/statements/kill.md)
- [OPTIMIZE](/docs/en/sql-reference/statements/optimize.md)
- [RENAME](/docs/en/sql-reference/statements/rename.md)
- [SET](/docs/en/sql-reference/statements/set.md)
- [SET ROLE](/docs/en/sql-reference/statements/set-role.md)
- [TRUNCATE](/docs/en/sql-reference/statements/truncate.md)
- [USE](/docs/en/sql-reference/statements/use.md)
- [EXPLAIN](/docs/en/sql-reference/statements/explain.md)

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@ -282,7 +282,7 @@ Each time a query is run with the same `JOIN`, the subquery is run again because
In some cases, it is more efficient to use [IN](../../../sql-reference/operators/in.md) instead of `JOIN`.
If you need a `JOIN` for joining with dimension tables (these are relatively small tables that contain dimension properties, such as names for advertising campaigns), a `JOIN` might not be very convenient due to the fact that the right table is re-accessed for every query. For such cases, there is an “external dictionaries” feature that you should use instead of `JOIN`. For more information, see the [External dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts.md) section.
If you need a `JOIN` for joining with dimension tables (these are relatively small tables that contain dimension properties, such as names for advertising campaigns), a `JOIN` might not be very convenient due to the fact that the right table is re-accessed for every query. For such cases, there is a “dictionaries” feature that you should use instead of `JOIN`. For more information, see the [Dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts.md) section.
### Memory Limitations

2
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@ -41,7 +41,7 @@ Purge default roles from a user:
SET DEFAULT ROLE NONE TO user
```
Set all the granted roles as default excepting some of them:
Set all the granted roles as default except for specific roles `role1` and `role2`:
``` sql
SET DEFAULT ROLE ALL EXCEPT role1, role2 TO user

2
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@ -198,7 +198,7 @@ Result:
## SHOW DICTIONARIES
Displays a list of [external dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md).
Displays a list of [Dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md).
``` sql
SHOW DICTIONARIES [FROM <db>] [LIKE '<pattern>'] [LIMIT <N>] [INTO OUTFILE <filename>] [FORMAT <format>]

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@ -39,3 +39,7 @@ You can’t use table functions if the [allow_ddl](../../operations/settings/per
| [s3](../../sql-reference/table-functions/s3.md) | Creates a [S3](../../engines/table-engines/integrations/s3.md)-engine table. |
| [sqlite](../../sql-reference/table-functions/sqlite.md) | Creates a [sqlite](../../engines/table-engines/integrations/sqlite.md)-engine table. |
:::note
Only these table functions are enabled in readonly mode :
null, view, viewIfPermitted, numbers, numbers_mt, generateRandom, values, cluster, clusterAllReplicas
:::

2
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@ -110,5 +110,5 @@ SELECT * FROM mysql('localhost:3306', 'test', 'test', 'bayonet', '123');
**See Also**
- [The ‘MySQL’ table engine](../../engines/table-engines/integrations/mysql.md)
- [Using MySQL as a source of external dictionary](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-mysql)
- [Using MySQL as a dictionary source](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-mysql)

2
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@ -101,5 +101,5 @@ SELECT * FROM odbc('DSN=mysqlconn', 'test', 'test')
## See Also
- [ODBC external dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-odbc)
- [ODBC dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-odbc)
- [ODBC table engine](../../engines/table-engines/integrations/odbc.md).

2
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@ -130,6 +130,6 @@ CREATE TABLE pg_table_schema_with_dots (a UInt32)
**See Also**
- [The PostgreSQL table engine](../../engines/table-engines/integrations/postgresql.md)
- [Using PostgreSQL as a source of external dictionary](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-postgresql)
- [Using PostgreSQL as a dictionary source](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-postgresql)
[Original article](https://clickhouse.com/docs/en/sql-reference/table-functions/postgresql/) <!--hide-->

4
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@ -7,8 +7,8 @@ slug: /ru/operations/system-tables/crash-log
Колонки:
- `event_date` ([Datetime](../../sql-reference/data-types/datetime.md)) — Дата события.
- `event_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — Время события.
- `event_date` ([DateTime](../../sql-reference/data-types/datetime.md)) — Дата события.
- `event_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — Время события.
- `timestamp_ns` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Время события с наносекундами.
- `signal` ([Int32](../../sql-reference/data-types/int-uint.md)) — Номер сигнала, пришедшего в поток.
- `thread_id` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Идентификатор треда.

4
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@ -15,7 +15,7 @@ slug: /ru/operations/system-tables/mutations
- `command` ([String](../../sql-reference/data-types/string.md)) — команда мутации (часть запроса после `ALTER TABLE [db.]table`).
- `create_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — дата и время создания мутации.
- `create_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — дата и время создания мутации.
- `block_numbers.partition_id` ([Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md))) — Для мутаций реплицированных таблиц массив содержит содержит номера партиций (по одной записи для каждой партиции). Для мутаций нереплицированных таблиц массив пустой.
@ -39,7 +39,7 @@ slug: /ru/operations/system-tables/mutations
- `latest_failed_part` ([String](../../sql-reference/data-types/string.md)) — имя последнего куска, мутация которого не удалась.
- `latest_fail_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — дата и время последней ошибки мутации.
- `latest_fail_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — дата и время последней ошибки мутации.
- `latest_fail_reason` ([String](../../sql-reference/data-types/string.md)) — причина последней ошибки мутации.

6
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@ -29,7 +29,7 @@ slug: /ru/operations/system-tables/replication_queue
- `MUTATE_PART` — применить одну или несколько мутаций к куску.
- `ALTER_METADATA` — применить изменения структуры таблицы в результате запросов с выражением `ALTER`.
- `create_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — дата и время отправки задачи на выполнение.
- `create_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — дата и время отправки задачи на выполнение.
- `required_quorum` ([UInt32](../../sql-reference/data-types/int-uint.md)) — количество реплик, ожидающих завершения задачи, с подтверждением о завершении. Этот столбец актуален только для задачи `GET_PARTS`.
@ -47,13 +47,13 @@ slug: /ru/operations/system-tables/replication_queue
- `last_exception` ([String](../../sql-reference/data-types/string.md)) — текст сообщения о последней возникшей ошибке, если таковые имеются.
- `last_attempt_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — дата и время последней попытки выполнить задачу.
- `last_attempt_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — дата и время последней попытки выполнить задачу.
- `num_postponed` ([UInt32](../../sql-reference/data-types/int-uint.md)) — количество отложенных задач.
- `postpone_reason` ([String](../../sql-reference/data-types/string.md)) — причина, по которой была отложена задача.
- `last_postpone_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — дата и время, когда была отложена задача в последний раз.
- `last_postpone_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — дата и время, когда была отложена задача в последний раз.
- `merge_type` ([String](../../sql-reference/data-types/string.md)) — тип текущего слияния. Пусто, если это мутация.

2
docs/ru/sql-reference/data-types/date32.md
View File

@ -6,7 +6,7 @@ sidebar_label: Date32
# Date32 {#data_type-datetime32}
Дата. Поддерживается такой же диапазон дат, как для типа [Datetime64](../../sql-reference/data-types/datetime64.md). Значение хранится в четырех байтах и соответствует числу дней с 1900-01-01 по 2299-12-31.
Дата. Поддерживается такой же диапазон дат, как для типа [DateTime64](../../sql-reference/data-types/datetime64.md). Значение хранится в четырех байтах и соответствует числу дней с 1900-01-01 по 2299-12-31.
**Пример**

4
docs/ru/sql-reference/functions/date-time-functions.md
View File

@ -602,7 +602,7 @@ date_trunc(unit, value[, timezone])
- Дата и время, отсеченные до указанной части.
Тип: [Datetime](../../sql-reference/data-types/datetime.md).
Тип: [DateTime](../../sql-reference/data-types/datetime.md).
**Примеры**
@ -913,7 +913,7 @@ now([timezone])
- Текущие дата и время.
Тип: [Datetime](../../sql-reference/data-types/datetime.md).
Тип: [DateTime](../../sql-reference/data-types/datetime.md).
**Пример**

2
docs/zh/introduction/distinctive-features.md
View File

@ -67,7 +67,7 @@ ClickHouse提供各种各样在允许牺牲数据精度的情况下对查询进
2. 基于数据的部分样本进行近似查询。这时，仅会从磁盘检索少部分比例的数据。
3. 不使用全部的聚合条件，通过随机选择有限个数据聚合条件进行聚合。这在数据聚合条件满足某些分布条件下，在提供相当准确的聚合结果的同时降低了计算资源的使用。
## Adaptive Join Algorithm {#adaptive-join-algorithm}
## 自适应连接算法 {#adaptive-join-algorithm}
ClickHouse支持自定义[JOIN](../sql-reference/statements/select/join.md)多个表，它更倾向于散列连接算法，如果有多个大表，则使用合并-连接算法

4
docs/zh/operations/system-tables/crash-log.md
View File

@ -7,8 +7,8 @@ slug: /zh/operations/system-tables/crash-log
列信息:
- `event_date` ([Datetime](../../sql-reference/data-types/datetime.md)) — 事件日期.
- `event_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — 事件时间.
- `event_date` ([DateTime](../../sql-reference/data-types/datetime.md)) — 事件日期.
- `event_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — 事件时间.
- `timestamp_ns` ([UInt64](../../sql-reference/data-types/int-uint.md)) — 以纳秒为单位的事件时间戳.
- `signal` ([Int32](../../sql-reference/data-types/int-uint.md)) — 信号编号.
- `thread_id` ([UInt64](../../sql-reference/data-types/int-uint.md)) — 线程ID.

4
docs/zh/operations/system-tables/mutations.md
View File

@ -15,7 +15,7 @@ slug: /zh/operations/system-tables/mutations
- `command` ([String](../../sql-reference/data-types/string.md)) — mutation命令字符串（`ALTER TABLE [db.]table`语句之后的部分)。
- `create_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — mutation命令提交执行的日期和时间。
- `create_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — mutation命令提交执行的日期和时间。
- `block_numbers.partition_id` ([Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md))) — 对于复制表的mutation，该数组包含分区的ID（每个分区都有一条记录）。对于非复制表的mutation，该数组为空。
@ -39,7 +39,7 @@ slug: /zh/operations/system-tables/mutations
- `latest_failed_part`([String](../../sql-reference/data-types/string.md)) — 最近不能mutation的part的名称。
- `latest_fail_time`([Datetime](../../sql-reference/data-types/datetime.md)) — 最近的一个mutation失败的时间。
- `latest_fail_time`([DateTime](../../sql-reference/data-types/datetime.md)) — 最近的一个mutation失败的时间。
- `latest_fail_reason`([String](../../sql-reference/data-types/string.md)) — 导致最近part的mutation失败的异常消息。

6
docs/zh/operations/system-tables/replication_queue.md
View File

@ -29,7 +29,7 @@ slug: /zh/operations/system-tables/replication_queue
- `MUTATE_PART` — 对分片应用一个或多个突变.
- `ALTER_METADATA` — 根据全局 /metadata 和 /columns 路径应用alter修改.
- `create_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — 提交任务执行的日期和时间.
- `create_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — 提交任务执行的日期和时间.
- `required_quorum` ([UInt32](../../sql-reference/data-types/int-uint.md)) — 等待任务完成并确认完成的副本数. 此列仅与 `GET_PARTS` 任务相关.
@ -47,13 +47,13 @@ slug: /zh/operations/system-tables/replication_queue
- `last_exception` ([String](../../sql-reference/data-types/string.md)) — 发生的最后一个错误的短信（如果有）.
- `last_attempt_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — 上次尝试任务的日期和时间.
- `last_attempt_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — 上次尝试任务的日期和时间.
- `num_postponed` ([UInt32](../../sql-reference/data-types/int-uint.md)) — 延期任务数.
- `postpone_reason` ([String](../../sql-reference/data-types/string.md)) — 任务延期的原因.
- `last_postpone_time` ([Datetime](../../sql-reference/data-types/datetime.md)) — 上次推迟任务的日期和时间.
- `last_postpone_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — 上次推迟任务的日期和时间.
- `merge_type` ([String](../../sql-reference/data-types/string.md)) — 当前合并的类型. 如果是突变则为空.

2
docs/zh/sql-reference/ansi.md
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@ -152,7 +152,7 @@ sidebar_label: "ANSI\u517C\u5BB9\u6027"
| F051-02 | TIME（时间）数据类型（并支持用于表达时间的字面量），小数秒精度至少为0 | 否 {.text-danger} | |
| F051-03 | 时间戳数据类型（并支持用于表达时间戳的字面量），小数秒精度至少为0和6 | 是 {.text-danger} | |
| F051-04 | 日期、时间和时间戳数据类型的比较谓词 | 是 {.text-success} | |
| F051-05 | Datetime 类型和字符串形式表达的时间之间的显式转换 | 是 {.text-success} | |
| F051-05 | DateTime 类型和字符串形式表达的时间之间的显式转换 | 是 {.text-success} | |
| F051-06 | CURRENT_DATE | 否 {.text-danger} | 使用`today()`替代 |
| F051-07 | LOCALTIME | 否 {.text-danger} | 使用`now()`替代 |
| F051-08 | LOCALTIMESTAMP | 否 {.text-danger} | |

2
docs/zh/sql-reference/data-types/datetime64.md
View File

@ -6,7 +6,7 @@ sidebar_position: 49
sidebar_label: DateTime64
---
# Datetime64 {#data_type-datetime64}
# DateTime64 {#data_type-datetime64}
此类型允许以日期（date）加时间（time）的形式来存储一个时刻的时间值，具有定义的亚秒精度

4
docs/zh/sql-reference/functions/date-time-functions.md
View File

@ -539,7 +539,7 @@ date_trunc(unit, value[, timezone])
- 按指定的单位向前取整后的DateTime。
类型: [Datetime](../../sql-reference/data-types/datetime.md).
类型: [DateTime](../../sql-reference/data-types/datetime.md).
**示例**
@ -850,7 +850,7 @@ now([timezone])
- 当前日期和时间。
类型: [Datetime](../../sql-reference/data-types/datetime.md).
类型: [DateTime](../../sql-reference/data-types/datetime.md).
**示例**

3
programs/client/Client.cpp
View File

@ -243,6 +243,7 @@ try
registerAggregateFunctions();
processConfig();
initTtyBuffer(toProgressOption(config().getString("progress", "default")));
/// Includes delayed_interactive.
if (is_interactive)
@ -1088,8 +1089,6 @@ void Client::processConfig()
}
else
{
std::string progress = config().getString("progress", "tty");
need_render_progress = (Poco::icompare(progress, "off") && Poco::icompare(progress, "no") && Poco::icompare(progress, "false") && Poco::icompare(progress, "0"));
echo_queries = config().getBool("echo", false);
ignore_error = config().getBool("ignore-error", false);

2
programs/git-import/git-import.cpp
View File

@ -351,7 +351,7 @@ struct LineChange
++pos;
}
indent = std::max(255U, num_spaces);
indent = std::min(255U, num_spaces);
line.assign(pos, end);
if (pos == end)

12
programs/keeper/Keeper.cpp
View File

@ -149,19 +149,7 @@ std::string getUserName(uid_t user_id)
Poco::Net::SocketAddress Keeper::socketBindListen(Poco::Net::ServerSocket & socket, const std::string & host, UInt16 port, [[maybe_unused]] bool secure) const
{
auto address = makeSocketAddress(host, port, &logger());
#if !defined(POCO_CLICKHOUSE_PATCH) || POCO_VERSION < 0x01090100
if (secure)
/// Bug in old (<1.9.1) poco, listen() after bind() with reusePort param will fail because have no implementation in SecureServerSocketImpl
/// https://github.com/pocoproject/poco/pull/2257
socket.bind(address, /* reuseAddress = */ true);
else
#endif
#if POCO_VERSION < 0x01080000
socket.bind(address, /* reuseAddress = */ true);
#else
socket.bind(address, /* reuseAddress = */ true, /* reusePort = */ config().getBool("listen_reuse_port", false));
#endif
socket.listen(/* backlog = */ config().getUInt("listen_backlog", 64));
return address;

3
programs/library-bridge/ExternalDictionaryLibraryHandler.cpp
View File

@ -1,7 +1,6 @@
#include "ExternalDictionaryLibraryHandler.h"
#include <base/scope_guard.h>
#include <base/bit_cast.h>
#include <base/find_symbols.h>
#include <IO/ReadHelpers.h>
@ -113,7 +112,7 @@ Block ExternalDictionaryLibraryHandler::loadAll()
Block ExternalDictionaryLibraryHandler::loadIds(const std::vector<uint64_t> & ids)
{
const ExternalDictionaryLibraryAPI::VectorUInt64 ids_data{bit_cast<decltype(ExternalDictionaryLibraryAPI::VectorUInt64::data)>(ids.data()), ids.size()};
const ExternalDictionaryLibraryAPI::VectorUInt64 ids_data{std::bit_cast<decltype(ExternalDictionaryLibraryAPI::VectorUInt64::data)>(ids.data()), ids.size()};
auto columns_holder = std::make_unique<ExternalDictionaryLibraryAPI::CString[]>(attributes_names.size());
ExternalDictionaryLibraryAPI::CStrings columns_pass{static_cast<decltype(ExternalDictionaryLibraryAPI::CStrings::data)>(columns_holder.get()), attributes_names.size()};

1
programs/library-bridge/ExternalDictionaryLibraryUtils.h
View File

@ -2,7 +2,6 @@
#include <Common/StringUtils/StringUtils.h>
#include <Core/Block.h>
#include <base/bit_cast.h>
#include <base/range.h>
#include "ExternalDictionaryLibraryAPI.h"

7
programs/local/LocalServer.cpp
View File

@ -37,6 +37,7 @@
#include <AggregateFunctions/registerAggregateFunctions.h>
#include <TableFunctions/registerTableFunctions.h>
#include <Storages/registerStorages.h>
#include <Storages/NamedCollections.h>
#include <Dictionaries/registerDictionaries.h>
#include <Disks/registerDisks.h>
#include <Formats/registerFormats.h>
@ -118,6 +119,8 @@ void LocalServer::initialize(Poco::Util::Application & self)
config().getUInt("max_io_thread_pool_size", 100),
config().getUInt("max_io_thread_pool_free_size", 0),
config().getUInt("io_thread_pool_queue_size", 10000));
NamedCollectionFactory::instance().initialize(config());
}
@ -414,6 +417,8 @@ try
registerFormats();
processConfig();
initTtyBuffer(toProgressOption(config().getString("progress", "default")));
applyCmdSettings(global_context);
if (is_interactive)
@ -489,8 +494,6 @@ void LocalServer::processConfig()
}
else
{
std::string progress = config().getString("progress", "tty");
need_render_progress = (Poco::icompare(progress, "off") && Poco::icompare(progress, "no") && Poco::icompare(progress, "false") && Poco::icompare(progress, "0"));
echo_queries = config().hasOption("echo") || config().hasOption("verbose");
ignore_error = config().getBool("ignore-error", false);
is_multiquery = true;

5
programs/obfuscator/Obfuscator.cpp
View File

@ -32,7 +32,6 @@
#include <Core/Block.h>
#include <base/StringRef.h>
#include <Common/DateLUT.h>
#include <base/bit_cast.h>
#include <IO/ReadBufferFromFileDescriptor.h>
#include <IO/WriteBufferFromFileDescriptor.h>
#include <IO/ReadBufferFromFile.h>
@ -278,9 +277,9 @@ Float transformFloatMantissa(Float x, UInt64 seed)
using UInt = std::conditional_t<std::is_same_v<Float, Float32>, UInt32, UInt64>;
constexpr size_t mantissa_num_bits = std::is_same_v<Float, Float32> ? 23 : 52;
UInt x_uint = bit_cast<UInt>(x);
UInt x_uint = std::bit_cast<UInt>(x);
x_uint = static_cast<UInt>(feistelNetwork(x_uint, mantissa_num_bits, seed));
return bit_cast<Float>(x_uint);
return std::bit_cast<Float>(x_uint);
}

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