- Fixed an error that led to problems with updating dictionaries with the ODBC source. [#3825](https://github.com/ClickHouse/ClickHouse/issues/3825), [#3829](https://github.com/ClickHouse/ClickHouse/issues/3829)
- JIT compilation of aggregate functions now works with LowCardinality columns. [#3838](https://github.com/ClickHouse/ClickHouse/issues/3838)
- Added the `low_cardinality_allow_in_native_format` setting (enabled by default). When disabled, LowCardinality columns will be converted to ordinary columns for SELECT queries and ordinary columns will be expected for INSERT queries. [#3879](https://github.com/ClickHouse/ClickHouse/pull/3879)
-`DEFAULT` expressions are evaluated for missing fields when loading data in semi-structured input formats (`JSONEachRow`, `TSKV`). The feature is enabled with the `insert_sample_with_metadata` setting. [#3555](https://github.com/ClickHouse/ClickHouse/pull/3555)
- The `ALTER TABLE` query now has the `MODIFY ORDER BY` action for changing the sorting key when adding or removing a table column. This is useful for tables in the `MergeTree` family that perform additional tasks when merging based on this sorting key, such as `SummingMergeTree`, `AggregatingMergeTree`, and so on. [#3581](https://github.com/ClickHouse/ClickHouse/pull/3581) [#3755](https://github.com/ClickHouse/ClickHouse/pull/3755)
- For tables in the `MergeTree` family, now you can specify a different sorting key (`ORDER BY`) and index (`PRIMARY KEY`). The sorting key can be longer than the index. [#3581](https://github.com/ClickHouse/ClickHouse/pull/3581)
- Added the `hdfs` table function and the `HDFS` table engine for importing and exporting data to HDFS. [chenxing-xc](https://github.com/ClickHouse/ClickHouse/pull/3617)
- Added functions for working with base64: `base64Encode`, `base64Decode`, `tryBase64Decode`. [Alexander Krasheninnikov](https://github.com/ClickHouse/ClickHouse/pull/3350)
- Now you can use a parameter to configure the precision of the `uniqCombined` aggregate function (select the number of HyperLogLog cells). [#3406](https://github.com/ClickHouse/ClickHouse/pull/3406)
- Added the `system.contributors` table that contains the names of everyone who made commits in ClickHouse. [#3452](https://github.com/ClickHouse/ClickHouse/pull/3452)
- Added the ability to omit the partition for the `ALTER TABLE ... FREEZE` query in order to back up all partitions at once. [#3514](https://github.com/ClickHouse/ClickHouse/pull/3514)
- Added `dictGet` and `dictGetOrDefault` functions that don’t require specifying the type of return value. The type is determined automatically from the dictionary description. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3564)
- Now you can specify comments for a column in the table description and change it using `ALTER`. [#3377](https://github.com/ClickHouse/ClickHouse/pull/3377)
- Reading is supported for `Join` type tables with simple keys. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3728)
- Now you can specify the options `join_use_nulls`, `max_rows_in_join`, `max_bytes_in_join`, and `join_overflow_mode` when creating a `Join` type table. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3728)
- Added the `joinGet` function that allows you to use a `Join` type table like a dictionary. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3728)
- Added the `partition_key`, `sorting_key`, `primary_key`, and `sampling_key` columns to the `system.tables` table in order to provide information about table keys. [#3609](https://github.com/ClickHouse/ClickHouse/pull/3609)
- Added the `is_in_partition_key`, `is_in_sorting_key`, `is_in_primary_key`, and `is_in_sampling_key` columns to the `system.columns` table. [#3609](https://github.com/ClickHouse/ClickHouse/pull/3609)
- Added the `min_time` and `max_time` columns to the `system.parts` table. These columns are populated when the partitioning key is an expression consisting of `DateTime` columns. [Emmanuel Donin de Rosière](https://github.com/ClickHouse/ClickHouse/pull/3800)
- Fixes and performance improvements for the `LowCardinality` data type. `GROUP BY` using `LowCardinality(Nullable(...))`. Getting the values of `extremes`. Processing high-order functions. `LEFT ARRAY JOIN`. Distributed `GROUP BY`. Functions that return `Array`. Execution of `ORDER BY`. Writing to `Distributed` tables (nicelulu). Backward compatibility for `INSERT` queries from old clients that implement the `Native` protocol. Support for `LowCardinality` for `JOIN`. Improved performance when working in a single stream. [#3823](https://github.com/ClickHouse/ClickHouse/pull/3823) [#3803](https://github.com/ClickHouse/ClickHouse/pull/3803) [#3799](https://github.com/ClickHouse/ClickHouse/pull/3799) [#3769](https://github.com/ClickHouse/ClickHouse/pull/3769) [#3744](https://github.com/ClickHouse/ClickHouse/pull/3744) [#3681](https://github.com/ClickHouse/ClickHouse/pull/3681) [#3651](https://github.com/ClickHouse/ClickHouse/pull/3651) [#3649](https://github.com/ClickHouse/ClickHouse/pull/3649) [#3641](https://github.com/ClickHouse/ClickHouse/pull/3641) [#3632](https://github.com/ClickHouse/ClickHouse/pull/3632) [#3568](https://github.com/ClickHouse/ClickHouse/pull/3568) [#3523](https://github.com/ClickHouse/ClickHouse/pull/3523) [#3518](https://github.com/ClickHouse/ClickHouse/pull/3518)
- Fixed how the `select_sequential_consistency` option works. Previously, when this setting was enabled, an incomplete result was sometimes returned after beginning to write to a new partition. [#2863](https://github.com/ClickHouse/ClickHouse/pull/2863)
- Databases are correctly specified when executing DDL `ON CLUSTER` queries and `ALTER UPDATE/DELETE`. [#3772](https://github.com/ClickHouse/ClickHouse/pull/3772) [#3460](https://github.com/ClickHouse/ClickHouse/pull/3460)
- Databases are correctly specified for subqueries inside a VIEW. [#3521](https://github.com/ClickHouse/ClickHouse/pull/3521)
- Fixed a bug in `PREWHERE` with `FINAL` for `VersionedCollapsingMergeTree`. [7167bfd7](https://github.com/ClickHouse/ClickHouse/commit/7167bfd7b365538f7a91c4307ad77e552ab4e8c1)
- Now you can use `KILL QUERY` to cancel queries that have not started yet because they are waiting for the table to be locked. [#3517](https://github.com/ClickHouse/ClickHouse/pull/3517)
- Corrected date and time calculations if the clocks were moved back at midnight (this happens in Iran, and happened in Moscow from 1981 to 1983). Previously, this led to the time being reset a day earlier than necessary, and also caused incorrect formatting of the date and time in text format. [#3819](https://github.com/ClickHouse/ClickHouse/pull/3819)
- Fixed a race condition when simultaneously reading from a `MATERIALIZED VIEW` and deleting a `MATERIALIZED VIEW` due to not locking the internal `MATERIALIZED VIEW`. [#3404](https://github.com/ClickHouse/ClickHouse/pull/3404) [#3694](https://github.com/ClickHouse/ClickHouse/pull/3694)
- Fixed the error `Lock handler cannot be nullptr.` [#3689](https://github.com/ClickHouse/ClickHouse/pull/3689)
- Fixed query processing when the `compile_expressions` option is enabled (it’s enabled by default). Nondeterministic constant expressions like the `now` function are no longer unfolded. [#3457](https://github.com/ClickHouse/ClickHouse/pull/3457)
- Fixed an error when trying to insert an array with `NULL` elements in the `Values` format into a column of type `Array` without `Nullable` (if `input_format_values_interpret_expressions` = 1). [#3487](https://github.com/ClickHouse/ClickHouse/pull/3487) [#3503](https://github.com/ClickHouse/ClickHouse/pull/3503)
- Fixed continuous error logging in `DDLWorker` if ZooKeeper is not available. [8f50c620](https://github.com/ClickHouse/ClickHouse/commit/8f50c620334988b28018213ec0092fe6423847e2)
- Fixed the return type for `quantile*` functions from `Date` and `DateTime` types of arguments. [#3580](https://github.com/ClickHouse/ClickHouse/pull/3580)
- Fixed the `WITH` clause if it specifies a simple alias without expressions. [#3570](https://github.com/ClickHouse/ClickHouse/pull/3570)
- Fixed processing of queries with named sub-queries and qualified column names when `enable_optimize_predicate_expression` is enabled. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3588)
- Fixed the error `Attempt to attach to nullptr thread group` when working with materialized views. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3623)
- Fixed a crash when passing certain incorrect arguments to the `arrayReverse` function. [73e3a7b6](https://github.com/ClickHouse/ClickHouse/commit/73e3a7b662161d6005e7727d8a711b930386b871)
- Fixed the buffer overflow in the `extractURLParameter` function. Improved performance. Added correct processing of strings containing zero bytes. [141e9799](https://github.com/ClickHouse/ClickHouse/commit/141e9799e49201d84ea8e951d1bed4fb6d3dacb5)
- Fixed buffer overflow in the `lowerUTF8` and `upperUTF8` functions. Removed the ability to execute these functions over `FixedString` type arguments. [#3662](https://github.com/ClickHouse/ClickHouse/pull/3662)
- Fixed a rare race condition when deleting `MergeTree` tables. [#3680](https://github.com/ClickHouse/ClickHouse/pull/3680)
- Fixed a race condition when reading from `Buffer` tables and simultaneously performing `ALTER` or `DROP` on the target tables. [#3719](https://github.com/ClickHouse/ClickHouse/pull/3719)
- Fixed a segfault if the `max_temporary_non_const_columns` limit was exceeded. [#3788](https://github.com/ClickHouse/ClickHouse/pull/3788)
- The server does not write the processed configuration files to the `/etc/clickhouse-server/` directory. Instead, it saves them in the `preprocessed_configs` directory inside `path`. This means that the `/etc/clickhouse-server/` directory doesn’t have write access for the `clickhouse` user, which improves security. [#2443](https://github.com/ClickHouse/ClickHouse/pull/2443)
- The `min_merge_bytes_to_use_direct_io` option is set to 10 GiB by default. A merge that forms large parts of tables from the MergeTree family will be performed in `O_DIRECT` mode, which prevents excessive page cache eviction. [#3504](https://github.com/ClickHouse/ClickHouse/pull/3504)
- Accelerated server start when there is a very large number of tables. [#3398](https://github.com/ClickHouse/ClickHouse/pull/3398)
- Added a connection pool and HTTP `Keep-Alive` for connections between replicas. [#3594](https://github.com/ClickHouse/ClickHouse/pull/3594)
- If the query syntax is invalid, the `400 Bad Request` code is returned in the `HTTP` interface (500 was returned previously). [31bc680a](https://github.com/ClickHouse/ClickHouse/commit/31bc680ac5f4bb1d0360a8ba4696fa84bb47d6ab)
- The `join_default_strictness` option is set to `ALL` by default for compatibility. [120e2cbe](https://github.com/ClickHouse/ClickHouse/commit/120e2cbe2ff4fbad626c28042d9b28781c805afe)
- Removed logging to `stderr` from the `re2` library for invalid or complex regular expressions. [#3723](https://github.com/ClickHouse/ClickHouse/pull/3723)
- Added for the `Kafka` table engine: checks for subscriptions before beginning to read from Kafka; the kafka_max_block_size setting for the table. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3396)
- The `cityHash64`, `farmHash64`, `metroHash64`, `sipHash64`, `halfMD5`, `murmurHash2_32`, `murmurHash2_64`, `murmurHash3_32`, and `murmurHash3_64` functions now work for any number of arguments and for arguments in the form of tuples. [#3451](https://github.com/ClickHouse/ClickHouse/pull/3451) [#3519](https://github.com/ClickHouse/ClickHouse/pull/3519)
- The `arrayReverse` function now works with any types of arrays. [73e3a7b6](https://github.com/ClickHouse/ClickHouse/commit/73e3a7b662161d6005e7727d8a711b930386b871)
- Added an optional parameter: the slot size for the `timeSlots` function. [Kirill Shvakov](https://github.com/ClickHouse/ClickHouse/pull/3724)
- For `FULL` and `RIGHT JOIN`, the `max_block_size` setting is used for a stream of non-joined data from the right table. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3699)
- Added the `--secure` command line parameter in `clickhouse-benchmark` and `clickhouse-performance-test` to enable TLS. [#3688](https://github.com/ClickHouse/ClickHouse/pull/3688) [#3690](https://github.com/ClickHouse/ClickHouse/pull/3690)
- Type conversion when the structure of a `Buffer` type table does not match the structure of the destination table. [Vitaly Baranov](https://github.com/ClickHouse/ClickHouse/pull/3603)
- Added the `tcp_keep_alive_timeout` option to enable keep-alive packets after inactivity for the specified time interval. [#3441](https://github.com/ClickHouse/ClickHouse/pull/3441)
- Removed unnecessary quoting of values for the partition key in the `system.parts` table if it consists of a single column. [#3652](https://github.com/ClickHouse/ClickHouse/pull/3652)
- The modulo function works for `Date` and `DateTime` data types. [#3385](https://github.com/ClickHouse/ClickHouse/pull/3385)
- Added synonyms for the `POWER`, `LN`, `LCASE`, `UCASE`, `REPLACE`, `LOCATE`, `SUBSTR`, and `MID` functions. [#3774](https://github.com/ClickHouse/ClickHouse/pull/3774) [#3763](https://github.com/ClickHouse/ClickHouse/pull/3763) Some function names are case-insensitive for compatibility with the SQL standard. Added syntactic sugar `SUBSTRING(expr FROM start FOR length)` for compatibility with SQL. [#3804](https://github.com/ClickHouse/ClickHouse/pull/3804)
- Added the ability to `mlock` memory pages corresponding to `clickhouse-server` executable code to prevent it from being forced out of memory. This feature is disabled by default. [#3553](https://github.com/ClickHouse/ClickHouse/pull/3553)
- Improved performance when reading from `O_DIRECT` (with the `min_bytes_to_use_direct_io` option enabled). [#3405](https://github.com/ClickHouse/ClickHouse/pull/3405)
- Improved performance of the `dictGet...OrDefault` function for a constant key argument and a non-constant default argument. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3563)
- The `firstSignificantSubdomain` function now processes the domains `gov`, `mil`, and `edu`. [Igor Hatarist](https://github.com/ClickHouse/ClickHouse/pull/3601) Improved performance. [#3628](https://github.com/ClickHouse/ClickHouse/pull/3628)
- Ability to specify custom environment variables for starting `clickhouse-server` using the `SYS-V init.d` script by defining `CLICKHOUSE_PROGRAM_ENV` in `/etc/default/clickhouse`.
- Correct return code for the clickhouse-server init script. [#3516](https://github.com/ClickHouse/ClickHouse/pull/3516)
- The `system.metrics` table now has the `VersionInteger` metric, and `system.build_options` has the added line `VERSION_INTEGER`, which contains the numeric form of the ClickHouse version, such as `18016000`. [#3644](https://github.com/ClickHouse/ClickHouse/pull/3644)
- Removed the ability to compare the `Date` type with a number to avoid potential errors like `date = 2018-12-17`, where quotes around the date are omitted by mistake. [#3687](https://github.com/ClickHouse/ClickHouse/pull/3687)
- Fixed the behavior of stateful functions like `rowNumberInAllBlocks`. They previously output a result that was one number larger due to starting during query analysis. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3729)
- If the `force_restore_data` file can’t be deleted, an error message is displayed. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3794)
- Updated the `jemalloc` library, which fixes a potential memory leak. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3557)
- Profiling with `jemalloc` is enabled by default in order to debug builds. [2cc82f5c](https://github.com/ClickHouse/ClickHouse/commit/2cc82f5cbe266421cd4c1165286c2c47e5ffcb15)
- Added the ability to run integration tests when only `Docker` is installed on the system. [#3650](https://github.com/ClickHouse/ClickHouse/pull/3650)
- Added the fuzz expression test in SELECT queries. [#3442](https://github.com/ClickHouse/ClickHouse/pull/3442)
- Added a stress test for commits, which performs functional tests in parallel and in random order to detect more race conditions. [#3438](https://github.com/ClickHouse/ClickHouse/pull/3438)
- Improved the method for starting clickhouse-server in a Docker image. [Elghazal Ahmed](https://github.com/ClickHouse/ClickHouse/pull/3663)
- For a Docker image, added support for initializing databases using files in the `/docker-entrypoint-initdb.d` directory. [Konstantin Lebedev](https://github.com/ClickHouse/ClickHouse/pull/3695)
- Removed the ability to compare the `Date` type with a number. Instead of `toDate('2018-12-18') = 17883`, you must use explicit type conversion `= toDate(17883)` [#3687](https://github.com/ClickHouse/ClickHouse/pull/3687)
- Fixed an error that led to problems with updating dictionaries with the ODBC source. [#3825](https://github.com/ClickHouse/ClickHouse/issues/3825), [#3829](https://github.com/ClickHouse/ClickHouse/issues/3829)
- Databases are correctly specified when executing DDL `ON CLUSTER` queries. [#3460](https://github.com/ClickHouse/ClickHouse/pull/3460)
- Fixed a segfault if the `max_temporary_non_const_columns` limit was exceeded. [#3788](https://github.com/ClickHouse/ClickHouse/pull/3788)
- Fixed error in `dictGet...` function for dictionaries of type `range`, if one of the arguments is constant and other is not. [#3751](https://github.com/ClickHouse/ClickHouse/pull/3751)
- Fixed error that caused messages `netlink: '...': attribute type 1 has an invalid length` to be printed in Linux kernel log, that was happening only on fresh enough versions of Linux kernel. [#3749](https://github.com/ClickHouse/ClickHouse/pull/3749)
- Fixed excessive memory allocation when using large value of `max_query_size` setting (a memory chunk of `max_query_size` bytes was preallocated at once). [#3720](https://github.com/ClickHouse/ClickHouse/pull/3720)
- Fixed build with LLVM/Clang libraries of version 7 from the OS packages (these libraries are used for runtime query compilation). [#3582](https://github.com/ClickHouse/ClickHouse/pull/3582)
- Fixed cases when the ODBC bridge process did not terminate with the main server process. [#3642](https://github.com/ClickHouse/ClickHouse/pull/3642)
- Fixed synchronous insertion into the `Distributed` table with a columns list that differs from the column list of the remote table. [#3673](https://github.com/ClickHouse/ClickHouse/pull/3673)
- Fixed a rare race condition that can lead to a crash when dropping a MergeTree table. [#3643](https://github.com/ClickHouse/ClickHouse/pull/3643)
- Fixed a query deadlock in case when query thread creation fails with the `Resource temporarily unavailable` error. [#3643](https://github.com/ClickHouse/ClickHouse/pull/3643)
- Fixed parsing of the `ENGINE` clause when the `CREATE AS table` syntax was used and the `ENGINE` clause was specified before the `AS table` (the error resulted in ignoring the specified engine). [#3692](https://github.com/ClickHouse/ClickHouse/pull/3692)
- The size of memory chunk was overestimated while deserializing the column of type `Array(String)` that leads to “Memory limit exceeded” errors. The issue appeared in version 18.12.13. [#3589](https://github.com/ClickHouse/ClickHouse/issues/3589)
- Fixed the `Block structure mismatch in MergingSorted stream` error. [#3162](https://github.com/ClickHouse/ClickHouse/issues/3162)
- Fixed `ON CLUSTER` queries in case when secure connections were turned on in the cluster config (the `<secure>` flag). [#3465](https://github.com/ClickHouse/ClickHouse/pull/3465)
- Fixed an error in queries that used `SAMPLE`, `PREWHERE` and alias columns. [#3543](https://github.com/ClickHouse/ClickHouse/pull/3543)
- Fixed a rare `unknown compression method` error when the `min_bytes_to_use_direct_io` setting was enabled. [3544](https://github.com/ClickHouse/ClickHouse/pull/3544)
- Fixed performance regression of queries with `GROUP BY` of columns of UInt16 or Date type when executing on AMD EPYC processors. [Igor Lapko](https://github.com/ClickHouse/ClickHouse/pull/3512)
- Improvements for simplifying the Arcadia build. [#3475](https://github.com/ClickHouse/ClickHouse/pull/3475), [#3535](https://github.com/ClickHouse/ClickHouse/pull/3535)
- Fixed the error `Block structure mismatch in UNION stream: different number of columns` in LIMIT queries. [#2156](https://github.com/ClickHouse/ClickHouse/issues/2156)
- Fixed errors when merging data in tables containing arrays inside Nested structures. [#3397](https://github.com/ClickHouse/ClickHouse/pull/3397)
- Fixed incorrect query results if the `merge_tree_uniform_read_distribution` setting is disabled (it is enabled by default). [#3429](https://github.com/ClickHouse/ClickHouse/pull/3429)
- Fixed an error on inserts to a Distributed table in Native format. [#3411](https://github.com/ClickHouse/ClickHouse/issues/3411)
- The `compile_expressions` setting (JIT compilation of expressions) is disabled by default. [#3410](https://github.com/ClickHouse/ClickHouse/pull/3410)
- The `WITH CUBE` modifier for `GROUP BY` (the alternative syntax `GROUP BY CUBE(...)` is also available). [#3172](https://github.com/ClickHouse/ClickHouse/pull/3172)
- Added the `formatDateTime` function. [Alexandr Krasheninnikov](https://github.com/ClickHouse/ClickHouse/pull/2770)
- Added the `JDBC` table engine and `jdbc` table function (requires installing clickhouse-jdbc-bridge). [Alexandr Krasheninnikov](https://github.com/ClickHouse/ClickHouse/pull/3210)
- Added functions for working with the ISO week number: `toISOWeek`, `toISOYear`, `toStartOfISOYear`, and `toDayOfYear`. [#3146](https://github.com/ClickHouse/ClickHouse/pull/3146)
- Now you can use `Nullable` columns for `MySQL` and `ODBC` tables. [#3362](https://github.com/ClickHouse/ClickHouse/pull/3362)
- Nested data structures can be read as nested objects in `JSONEachRow` format. Added the `input_format_import_nested_json` setting. [Veloman Yunkan](https://github.com/ClickHouse/ClickHouse/pull/3144)
- Parallel processing is available for many `MATERIALIZED VIEW`s when inserting data. See the `parallel_view_processing` setting. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3208)
- Added the `SYSTEM FLUSH LOGS` query (forced log flushes to system tables such as `query_log`) [#3321](https://github.com/ClickHouse/ClickHouse/pull/3321)
- Now you can use pre-defined `database` and `table` macros when declaring `Replicated` tables. [#3251](https://github.com/ClickHouse/ClickHouse/pull/3251)
- Added the ability to read `Decimal` type values in engineering notation (indicating powers of ten). [#3153](https://github.com/ClickHouse/ClickHouse/pull/3153)
- Significantly reduced memory consumption for queries with `ORDER BY` and `LIMIT`. See the `max_bytes_before_remerge_sort` setting. [#3205](https://github.com/ClickHouse/ClickHouse/pull/3205)
- In the absence of `JOIN` (`LEFT`, `INNER`, …), `INNER JOIN` is assumed. [#3147](https://github.com/ClickHouse/ClickHouse/pull/3147)
- Qualified asterisks work correctly in queries with `JOIN`. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3202)
- The `ODBC` table engine correctly chooses the method for quoting identifiers in the SQL dialect of a remote database. [Alexandr Krasheninnikov](https://github.com/ClickHouse/ClickHouse/pull/3210)
- The `compile_expressions` setting (JIT compilation of expressions) is enabled by default.
- Fixed behavior for simultaneous DROP DATABASE/TABLE IF EXISTS and CREATE DATABASE/TABLE IF NOT EXISTS. Previously, a `CREATE DATABASE ... IF NOT EXISTS` query could return the error message “File … already exists”, and the `CREATE TABLE ... IF NOT EXISTS` and `DROP TABLE IF EXISTS` queries could return `Table ... is creating or attaching right now`. [#3101](https://github.com/ClickHouse/ClickHouse/pull/3101)
- LIKE and IN expressions with a constant right half are passed to the remote server when querying from MySQL or ODBC tables. [#3182](https://github.com/ClickHouse/ClickHouse/pull/3182)
- Comparisons with constant expressions in a WHERE clause are passed to the remote server when querying from MySQL and ODBC tables. Previously, only comparisons with constants were passed. [#3182](https://github.com/ClickHouse/ClickHouse/pull/3182)
- Correct calculation of row width in the terminal for `Pretty` formats, including strings with hieroglyphs. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3257).
-`ON CLUSTER` can be specified for `ALTER UPDATE` queries.
- Improved performance for reading data in `JSONEachRow` format. [#3332](https://github.com/ClickHouse/ClickHouse/pull/3332)
- Added synonyms for the `LENGTH` and `CHARACTER_LENGTH` functions for compatibility. The `CONCAT` function is no longer case-sensitive. [#3306](https://github.com/ClickHouse/ClickHouse/pull/3306)
- Added the `TIMESTAMP` synonym for the `DateTime` type. [#3390](https://github.com/ClickHouse/ClickHouse/pull/3390)
- There is always space reserved for query_id in the server logs, even if the log line is not related to a query. This makes it easier to parse server text logs with third-party tools.
- Memory consumption by a query is logged when it exceeds the next level of an integer number of gigabytes. [#3205](https://github.com/ClickHouse/ClickHouse/pull/3205)
- Added compatibility mode for the case when the client library that uses the Native protocol sends fewer columns by mistake than the server expects for the INSERT query. This scenario was possible when using the clickhouse-cpp library. Previously, this scenario caused the server to crash. [#3171](https://github.com/ClickHouse/ClickHouse/pull/3171)
- In a user-defined WHERE expression in `clickhouse-copier`, you can now use a `partition_key` alias (for additional filtering by source table partition). This is useful if the partitioning scheme changes during copying, but only changes slightly. [#3166](https://github.com/ClickHouse/ClickHouse/pull/3166)
- The workflow of the `Kafka` engine has been moved to a background thread pool in order to automatically reduce the speed of data reading at high loads. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3215).
- Support for reading `Tuple` and `Nested` values of structures like `struct` in the `Cap'n'Proto format`. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3216)
- The list of top-level domains for the `firstSignificantSubdomain` function now includes the domain `biz`. [decaseal](https://github.com/ClickHouse/ClickHouse/pull/3219)
- In the configuration of external dictionaries, `null_value` is interpreted as the value of the default data type. [#3330](https://github.com/ClickHouse/ClickHouse/pull/3330)
- Support for the `intDiv` and `intDivOrZero` functions for `Decimal`. [b48402e8](https://github.com/ClickHouse/ClickHouse/commit/b48402e8712e2b9b151e0eef8193811d433a1264)
- Support for the `Date`, `DateTime`, `UUID`, and `Decimal` types as a key for the `sumMap` aggregate function. [#3281](https://github.com/ClickHouse/ClickHouse/pull/3281)
- Support for the `Decimal` data type in external dictionaries. [#3324](https://github.com/ClickHouse/ClickHouse/pull/3324)
- Support for the `Decimal` data type in `SummingMergeTree` tables. [#3348](https://github.com/ClickHouse/ClickHouse/pull/3348)
- Added specializations for `UUID` in `if`. [#3366](https://github.com/ClickHouse/ClickHouse/pull/3366)
- Reduced the number of `open` and `close` system calls when reading from a `MergeTree table`. [#3283](https://github.com/ClickHouse/ClickHouse/pull/3283)
- A `TRUNCATE TABLE` query can be executed on any replica (the query is passed to the leader replica). [Kirill Shvakov](https://github.com/ClickHouse/ClickHouse/pull/3375)
- Fixed an issue with `Dictionary` tables for `range_hashed` dictionaries. This error occurred in version 18.12.17. [#1702](https://github.com/ClickHouse/ClickHouse/pull/1702)
- Fixed an error when loading `range_hashed` dictionaries (the message `Unsupported type Nullable (...)`). This error occurred in version 18.12.17. [#3362](https://github.com/ClickHouse/ClickHouse/pull/3362)
- Fixed errors in the `pointInPolygon` function due to the accumulation of inaccurate calculations for polygons with a large number of vertices located close to each other. [#3331](https://github.com/ClickHouse/ClickHouse/pull/3331) [#3341](https://github.com/ClickHouse/ClickHouse/pull/3341)
- If after merging data parts, the checksum for the resulting part differs from the result of the same merge in another replica, the result of the merge is deleted and the data part is downloaded from the other replica (this is the correct behavior). But after downloading the data part, it couldn’t be added to the working set because of an error that the part already exists (because the data part was deleted with some delay after the merge). This led to cyclical attempts to download the same data. [#3194](https://github.com/ClickHouse/ClickHouse/pull/3194)
- Fixed incorrect calculation of total memory consumption by queries (because of incorrect calculation, the `max_memory_usage_for_all_queries` setting worked incorrectly and the `MemoryTracking` metric had an incorrect value). This error occurred in version 18.12.13. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3344)
- Fixed the functionality of `CREATE TABLE ... ON CLUSTER ... AS SELECT ...` This error occurred in version 18.12.13. [#3247](https://github.com/ClickHouse/ClickHouse/pull/3247)
- Fixed unnecessary preparation of data structures for `JOIN`s on the server that initiates the query if the `JOIN` is only performed on remote servers. [#3340](https://github.com/ClickHouse/ClickHouse/pull/3340)
- Fixed bugs in the `Kafka` engine: deadlocks after exceptions when starting to read data, and locks upon completion [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3215).
- For `Kafka` tables, the optional `schema` parameter was not passed (the schema of the `Cap'n'Proto` format). [Vojtech Splichal](https://github.com/ClickHouse/ClickHouse/pull/3150)
- If the ensemble of ZooKeeper servers has servers that accept the connection but then immediately close it instead of responding to the handshake, ClickHouse chooses to connect another server. Previously, this produced the error `Cannot read all data. Bytes read: 0. Bytes expected: 4.` and the server couldn’t start. [8218cf3a](https://github.com/ClickHouse/ClickHouse/commit/8218cf3a5f39a43401953769d6d12a0bb8d29da9)
- If the ensemble of ZooKeeper servers contains servers for which the DNS query returns an error, these servers are ignored. [17b8e209](https://github.com/ClickHouse/ClickHouse/commit/17b8e209221061325ad7ba0539f03c6e65f87f29)
- Fixed type conversion between `Date` and `DateTime` when inserting data in the `VALUES` format (if `input_format_values_interpret_expressions = 1`). Previously, the conversion was performed between the numerical value of the number of days in Unix Epoch time and the Unix timestamp, which led to unexpected results. [#3229](https://github.com/ClickHouse/ClickHouse/pull/3229)
- Corrected type conversion between `Decimal` and integer numbers. [#3211](https://github.com/ClickHouse/ClickHouse/pull/3211)
- Fixed a parsing error in CSV format with floating-point numbers if a non-default CSV separator is used, such as `;` [#3155](https://github.com/ClickHouse/ClickHouse/pull/3155)
- Fixed the `arrayCumSumNonNegative` function (it does not accumulate negative values if the accumulator is less than zero). [Aleksey Studnev](https://github.com/ClickHouse/ClickHouse/pull/3163)
- Fixed a crash when dividing a `Decimal` value by zero. [69dd6609](https://github.com/ClickHouse/ClickHouse/commit/69dd6609193beb4e7acd3e6ad216eca0ccfb8179)
- Fixed the segfault during `GROUP BY` on `Decimal128`. [3359ba06](https://github.com/ClickHouse/ClickHouse/commit/3359ba06c39fcd05bfdb87d6c64154819621e13a)
- The `log_query_threads` setting (logging information about each thread of query execution) now takes effect only if the `log_queries` option (logging information about queries) is set to 1. Since the `log_query_threads` option is enabled by default, information about threads was previously logged even if query logging was disabled. [#3241](https://github.com/ClickHouse/ClickHouse/pull/3241)
- Fixed an error in the distributed operation of the quantiles aggregate function (the error message `Not found column quantile...`). [292a8855](https://github.com/ClickHouse/ClickHouse/commit/292a885533b8e3b41ce8993867069d14cbd5a664)
- Fixed the compatibility problem when working on a cluster of version 18.12.17 servers and older servers at the same time. For distributed queries with GROUP BY keys of both fixed and non-fixed length, if there was a large amount of data to aggregate, the returned data was not always fully aggregated (two different rows contained the same aggregation keys). [#3254](https://github.com/ClickHouse/ClickHouse/pull/3254)
- Fixed handling of substitutions in `clickhouse-performance-test`, if the query contains only part of the substitutions declared in the test. [#3263](https://github.com/ClickHouse/ClickHouse/pull/3263)
- Fixed an error when using `FINAL` with `PREWHERE`. [#3298](https://github.com/ClickHouse/ClickHouse/pull/3298)
- Fixed an error when using `PREWHERE` over columns that were added during `ALTER`. [#3298](https://github.com/ClickHouse/ClickHouse/pull/3298)
- Added a check for the absence of `arrayJoin` for `DEFAULT` and `MATERIALIZED` expressions. Previously, `arrayJoin` led to an error when inserting data. [#3337](https://github.com/ClickHouse/ClickHouse/pull/3337)
- Added a check for the absence of `arrayJoin` in a `PREWHERE` clause. Previously, this led to messages like `Size ... doesn't match` or `Unknown compression method` when executing queries. [#3357](https://github.com/ClickHouse/ClickHouse/pull/3357)
- Fixed segfault that could occur in rare cases after optimization that replaced AND chains from equality evaluations with the corresponding IN expression. [liuyimin-bytedance](https://github.com/ClickHouse/ClickHouse/pull/3339)
- Minor corrections to `clickhouse-benchmark`: previously, client information was not sent to the server; now the number of queries executed is calculated more accurately when shutting down and for limiting the number of iterations. [#3351](https://github.com/ClickHouse/ClickHouse/pull/3351) [#3352](https://github.com/ClickHouse/ClickHouse/pull/3352)
- Removed the `allow_experimental_decimal_type` option. The `Decimal` data type is available for default use. [#3329](https://github.com/ClickHouse/ClickHouse/pull/3329)
-`invalidate_query` (the ability to specify a query to check whether an external dictionary needs to be updated) is implemented for the `clickhouse` source. [#3126](https://github.com/ClickHouse/ClickHouse/pull/3126)
- Added the ability to use `UInt*`, `Int*`, and `DateTime` data types (along with the `Date` type) as a `range_hashed` external dictionary key that defines the boundaries of ranges. Now `NULL` can be used to designate an open range. [Vasily Nemkov](https://github.com/ClickHouse/ClickHouse/pull/3123)
- Fixed incompatibility (unnecessary dependency on the `glibc` version) that made it impossible to run ClickHouse on `Ubuntu Precise` and older versions. The incompatibility arose in version 18.12.13. [#3130](https://github.com/ClickHouse/ClickHouse/pull/3130)
- Fixed a minor issue with backwards compatibility that appeared when working with a cluster of replicas on versions earlier than 18.12.13 and simultaneously creating a new replica of a table on a server with a newer version (shown in the message `Can not clone replica, because the ... updated to new ClickHouse version`, which is logical, but shouldn’t happen). [#3122](https://github.com/ClickHouse/ClickHouse/pull/3122)
- The `enable_optimize_predicate_expression` option is enabled by default (which is rather optimistic). If query analysis errors occur that are related to searching for the column names, set `enable_optimize_predicate_expression` to 0. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3107)
- Added support for `ALTER UPDATE` queries. [#3035](https://github.com/ClickHouse/ClickHouse/pull/3035)
- Added the `allow_ddl` option, which restricts the user’s access to DDL queries. [#3104](https://github.com/ClickHouse/ClickHouse/pull/3104)
- Added the `min_merge_bytes_to_use_direct_io` option for `MergeTree` engines, which allows you to set a threshold for the total size of the merge (when above the threshold, data part files will be handled using O_DIRECT). [#3117](https://github.com/ClickHouse/ClickHouse/pull/3117)
- The `system.merges` system table now contains the `partition_id` column. [#3099](https://github.com/ClickHouse/ClickHouse/pull/3099)
- Added a check for the sizes of arrays that are elements of `Nested` type fields when inserting. [#3118](https://github.com/ClickHouse/ClickHouse/pull/3118)
- Fixed an error updating external dictionaries with the `ODBC` source and `hashed` storage. This error occurred in version 18.12.13.
- Fixed a crash when creating a temporary table from a query with an `IN` condition. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3098)
- Fixed an error in aggregate functions for arrays that can have `NULL` elements. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3097)
- Added the `DECIMAL(digits, scale)` data type (`Decimal32(scale)`, `Decimal64(scale)`, `Decimal128(scale)`). To enable it, use the setting `allow_experimental_decimal_type`. [#2846](https://github.com/ClickHouse/ClickHouse/pull/2846) [#2970](https://github.com/ClickHouse/ClickHouse/pull/2970) [#3008](https://github.com/ClickHouse/ClickHouse/pull/3008) [#3047](https://github.com/ClickHouse/ClickHouse/pull/3047)
- New `WITH ROLLUP` modifier for `GROUP BY` (alternative syntax: `GROUP BY ROLLUP(...)`). [#2948](https://github.com/ClickHouse/ClickHouse/pull/2948)
- In queries with JOIN, the star character expands to a list of columns in all tables, in compliance with the SQL standard. You can restore the old behavior by setting `asterisk_left_columns_only` to 1 on the user configuration level. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2787)
- Added support for JOIN with table functions. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2907)
- Autocomplete by pressing Tab in clickhouse-client. [Sergey Shcherbin](https://github.com/ClickHouse/ClickHouse/pull/2447)
- Ctrl+C in clickhouse-client clears a query that was entered. [#2877](https://github.com/ClickHouse/ClickHouse/pull/2877)
- Added the `join_default_strictness` setting (values: `"`, `'any'`, `'all'`). This allows you to not specify `ANY` or `ALL` for `JOIN`. [#2982](https://github.com/ClickHouse/ClickHouse/pull/2982)
- Each line of the server log related to query processing shows the query ID. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Now you can get query execution logs in clickhouse-client (use the `send_logs_level` setting). With distributed query processing, logs are cascaded from all the servers. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `system.query_log` and `system.processes` (`SHOW PROCESSLIST`) tables now have information about all changed settings when you run a query (the nested structure of the `Settings` data). Added the `log_query_settings` setting. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `system.query_log` and `system.processes` tables now show information about the number of threads that are participating in query execution (see the `thread_numbers` column). [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Added `ProfileEvents` counters that measure the time spent on reading and writing over the network and reading and writing to disk, the number of network errors, and the time spent waiting when network bandwidth is limited. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Added `ProfileEvents`counters that contain the system metrics from rusage (you can use them to get information about CPU usage in userspace and the kernel, page faults, and context switches), as well as taskstats metrics (use these to obtain information about I/O wait time, CPU wait time, and the amount of data read and recorded, both with and without page cache). [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `ProfileEvents` counters are applied globally and for each query, as well as for each query execution thread, which allows you to profile resource consumption by query in detail. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Added the `system.query_thread_log` table, which contains information about each query execution thread. Added the `log_query_threads` setting. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `system.metrics` and `system.events` tables now have built-in documentation. [#3016](https://github.com/ClickHouse/ClickHouse/pull/3016)
- Now you can add (merge) states of aggregate functions by using the plus operator, and multiply the states of aggregate functions by a nonnegative constant. [#3062](https://github.com/ClickHouse/ClickHouse/pull/3062) [#3034](https://github.com/ClickHouse/ClickHouse/pull/3034)
- Tables in the MergeTree family now have the virtual column `_partition_id`. [#3089](https://github.com/ClickHouse/ClickHouse/pull/3089)
- Added the `LowCardinality(T)` data type. This data type automatically creates a local dictionary of values and allows data processing without unpacking the dictionary. [#2830](https://github.com/ClickHouse/ClickHouse/pull/2830)
- Added a cache of JIT-compiled functions and a counter for the number of uses before compiling. To JIT compile expressions, enable the `compile_expressions` setting. [#2990](https://github.com/ClickHouse/ClickHouse/pull/2990) [#3077](https://github.com/ClickHouse/ClickHouse/pull/3077)
- Fixed the problem with unlimited accumulation of the replication log when there are abandoned replicas. Added an effective recovery mode for replicas with a long lag.
- Improved performance of `GROUP BY` with multiple aggregation fields when one of them is string and the others are fixed length.
- Improved performance when using `PREWHERE` and with implicit transfer of expressions in `PREWHERE`.
- Increased performance and reduced memory consumption for queries to `system.tables` and `system.columns` when there is a very large number of tables on a single server. [#2953](https://github.com/ClickHouse/ClickHouse/pull/2953)
- Fixed a performance problem in the case of a large stream of queries that result in an error (the `_dl_addr` function is visible in `perf top`, but the server isn’t using much CPU). [#2938](https://github.com/ClickHouse/ClickHouse/pull/2938)
- Conditions are cast into the View (when `enable_optimize_predicate_expression` is enabled). [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2907)
- Improvements to the functionality for the `UUID` data type. [#3074](https://github.com/ClickHouse/ClickHouse/pull/3074) [#2985](https://github.com/ClickHouse/ClickHouse/pull/2985)
- The `UUID` data type is supported in The-Alchemist dictionaries. [#2822](https://github.com/ClickHouse/ClickHouse/pull/2822)
- The `visitParamExtractRaw` function works correctly with nested structures. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2974)
- When the `input_format_skip_unknown_fields` setting is enabled, object fields in `JSONEachRow` format are skipped correctly. [BlahGeek](https://github.com/ClickHouse/ClickHouse/pull/2958)
- For a `CASE` expression with conditions, you can now omit `ELSE`, which is equivalent to `ELSE NULL`. [#2920](https://github.com/ClickHouse/ClickHouse/pull/2920)
- Increased the size of the queue to write to system tables, so the `SystemLog parameter queue is full` error doesn’t happen as often.
- The `windowFunnel` aggregate function now supports events that meet multiple conditions. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2801)
- Duplicate columns can be used in a `USING` clause for `JOIN`. [#3006](https://github.com/ClickHouse/ClickHouse/pull/3006)
-`Pretty` formats now have a limit on column alignment by width. Use the `output_format_pretty_max_column_pad_width` setting. If a value is wider, it will still be displayed in its entirety, but the other cells in the table will not be too wide. [#3003](https://github.com/ClickHouse/ClickHouse/pull/3003)
- The `odbc` table function now allows you to specify the database/schema name. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2885)
- Added the ability to use a username specified in the `clickhouse-client` config file. [Vladimir Kozbin](https://github.com/ClickHouse/ClickHouse/pull/2909)
- The `ZooKeeperExceptions` counter has been split into three counters: `ZooKeeperUserExceptions`, `ZooKeeperHardwareExceptions`, and `ZooKeeperOtherExceptions`.
-`ALTER DELETE` queries work for materialized views.
- Added randomization when running the cleanup thread periodically for `ReplicatedMergeTree` tables in order to avoid periodic load spikes when there are a very large number of `ReplicatedMergeTree` tables.
- Fixed an issue with `Dictionary` tables (throws the `Size of offsets doesn't match size of column` or `Unknown compression method` exception). This bug appeared in version 18.10.3. [#2913](https://github.com/ClickHouse/ClickHouse/issues/2913)
- Fixed a bug when merging `CollapsingMergeTree` tables if one of the data parts is empty (these parts are formed during merge or `ALTER DELETE` if all data was deleted), and the `vertical` algorithm was used for the merge. [#3049](https://github.com/ClickHouse/ClickHouse/pull/3049)
- Fixed a race condition during `DROP` or `TRUNCATE` for `Memory` tables with a simultaneous `SELECT`, which could lead to server crashes. This bug appeared in version 1.1.54388. [#3038](https://github.com/ClickHouse/ClickHouse/pull/3038)
- Fixed the possibility of data loss when inserting in `Replicated` tables if the `Session is expired` error is returned (data loss can be detected by the `ReplicatedDataLoss` metric). This error occurred in version 1.1.54378. [#2939](https://github.com/ClickHouse/ClickHouse/pull/2939) [#2949](https://github.com/ClickHouse/ClickHouse/pull/2949) [#2964](https://github.com/ClickHouse/ClickHouse/pull/2964)
- Fixed a segfault during `JOIN ... ON`. [#3000](https://github.com/ClickHouse/ClickHouse/pull/3000)
- Fixed the error searching column names when the `WHERE` expression consists entirely of a qualified column name, such as `WHERE table.column`. [#2994](https://github.com/ClickHouse/ClickHouse/pull/2994)
- Fixed the “Not found column” error that occurred when executing distributed queries if a single column consisting of an IN expression with a subquery is requested from a remote server. [#3087](https://github.com/ClickHouse/ClickHouse/pull/3087)
- Fixed the `Block structure mismatch in UNION stream: different number of columns` error that occurred for distributed queries if one of the shards is local and the other is not, and optimization of the move to `PREWHERE` is triggered. [#2226](https://github.com/ClickHouse/ClickHouse/pull/2226) [#3037](https://github.com/ClickHouse/ClickHouse/pull/3037) [#3055](https://github.com/ClickHouse/ClickHouse/pull/3055) [#3065](https://github.com/ClickHouse/ClickHouse/pull/3065) [#3073](https://github.com/ClickHouse/ClickHouse/pull/3073) [#3090](https://github.com/ClickHouse/ClickHouse/pull/3090) [#3093](https://github.com/ClickHouse/ClickHouse/pull/3093)
- Fixed the `pointInPolygon` function for certain cases of non-convex polygons. [#2910](https://github.com/ClickHouse/ClickHouse/pull/2910)
- Fixed the incorrect result when comparing `nan` with integers. [#3024](https://github.com/ClickHouse/ClickHouse/pull/3024)
- Fixed an error in the `zlib-ng` library that could lead to segfault in rare cases. [#2854](https://github.com/ClickHouse/ClickHouse/pull/2854)
- Fixed a memory leak when inserting into a table with `AggregateFunction` columns, if the state of the aggregate function is not simple (allocates memory separately), and if a single insertion request results in multiple small blocks. [#3084](https://github.com/ClickHouse/ClickHouse/pull/3084)
- Fixed the possibility of a segfault when comparing tuples made up of certain non-trivial types, such as tuples. [#2989](https://github.com/ClickHouse/ClickHouse/pull/2989)
- Fixed an error in the `arrayDistinct` function for `Nullable` array elements. [#2845](https://github.com/ClickHouse/ClickHouse/pull/2845) [#2937](https://github.com/ClickHouse/ClickHouse/pull/2937)
- The `enable_optimize_predicate_expression` option now correctly supports cases with `SELECT *`. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2929)
- Fixed potential blocking when working with ZooKeeper.
- Fixed incorrect code for adding nested data structures in a `SummingMergeTree`.
- When allocating memory for states of aggregate functions, alignment is correctly taken into account, which makes it possible to use operations that require alignment when implementing states of aggregate functions. [chenxing-xc](https://github.com/ClickHouse/ClickHouse/pull/2808)
- Safe use of ODBC data sources. Interaction with ODBC drivers uses a separate `clickhouse-odbc-bridge` process. Errors in third-party ODBC drivers no longer cause problems with server stability or vulnerabilities. [#2828](https://github.com/ClickHouse/ClickHouse/pull/2828) [#2879](https://github.com/ClickHouse/ClickHouse/pull/2879) [#2886](https://github.com/ClickHouse/ClickHouse/pull/2886) [#2893](https://github.com/ClickHouse/ClickHouse/pull/2893) [#2921](https://github.com/ClickHouse/ClickHouse/pull/2921)
- Fixed incorrect validation of the file path in the `catBoostPool` table function. [#2894](https://github.com/ClickHouse/ClickHouse/pull/2894)
- The contents of system tables (`tables`, `databases`, `parts`, `columns`, `parts_columns`, `merges`, `mutations`, `replicas`, and `replication_queue`) are filtered according to the user’s configured access to databases (`allow_databases`). [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2856)
- In queries with JOIN, the star character expands to a list of columns in all tables, in compliance with the SQL standard. You can restore the old behavior by setting `asterisk_left_columns_only` to 1 on the user configuration level.
- Most integration tests can now be run by commit.
- Code style checks can also be run by commit.
- The `memcpy` implementation is chosen correctly when building on CentOS7/Fedora. [Etienne Champetier](https://github.com/ClickHouse/ClickHouse/pull/2912)
- When using clang to build, some warnings from `-Weverything` have been added, in addition to the regular `-Wall-Wextra -Werror`. [#2957](https://github.com/ClickHouse/ClickHouse/pull/2957)
- HTTPS can be used for replication. [#2760](https://github.com/ClickHouse/ClickHouse/pull/2760)
- Added the functions `murmurHash2_64`, `murmurHash3_32`, `murmurHash3_64`, and `murmurHash3_128` in addition to the existing `murmurHash2_32`. [#2791](https://github.com/ClickHouse/ClickHouse/pull/2791)
- Support for Nullable types in the ClickHouse ODBC driver (`ODBCDriver2` output format). [#2834](https://github.com/ClickHouse/ClickHouse/pull/2834)
- Clusters can be removed without restarting the server when they are deleted from the config files. [#2777](https://github.com/ClickHouse/ClickHouse/pull/2777)
- External dictionaries can be removed without restarting the server when they are removed from config files. [#2779](https://github.com/ClickHouse/ClickHouse/pull/2779)
- Improvements for the `UUID` data type (not yet complete). [#2618](https://github.com/ClickHouse/ClickHouse/pull/2618)
- Support for empty parts after merges in the `SummingMergeTree`, `CollapsingMergeTree` and `VersionedCollapsingMergeTree` engines. [#2815](https://github.com/ClickHouse/ClickHouse/pull/2815)
- Old records of completed mutations are deleted (`ALTER DELETE`). [#2784](https://github.com/ClickHouse/ClickHouse/pull/2784)
- Added the `system.merge_tree_settings` table. [Kirill Shvakov](https://github.com/ClickHouse/ClickHouse/pull/2841)
- The `system.tables` table now has dependency columns: `dependencies_database` and `dependencies_table`. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2851)
- Added the `max_fetch_partition_retries_count` setting. [#2831](https://github.com/ClickHouse/ClickHouse/pull/2831)
- Added the `prefer_localhost_replica` setting for disabling the preference for a local replica and going to a local replica without inter-process interaction. [#2832](https://github.com/ClickHouse/ClickHouse/pull/2832)
- The `quantileExact` aggregate function returns `nan` in the case of aggregation on an empty `Float32` or `Float64` set. [Sundy Li](https://github.com/ClickHouse/ClickHouse/pull/2855)
- Removed unnecessary escaping of the connection string parameters for ODBC, which made it impossible to establish a connection. This error occurred in version 18.6.0.
- Fixed the logic for processing `REPLACE PARTITION` commands in the replication queue. If there are two `REPLACE` commands for the same partition, the incorrect logic could cause one of them to remain in the replication queue and not be executed. [#2814](https://github.com/ClickHouse/ClickHouse/pull/2814)
- Fixed a merge bug when all data parts were empty (parts that were formed from a merge or from `ALTER DELETE` if all data was deleted). This bug appeared in version 18.1.0. [#2930](https://github.com/ClickHouse/ClickHouse/pull/2930)
- Fixed an error for concurrent `Set` or `Join`. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2823)
- Fixed the `Block structure mismatch in UNION stream: different number of columns` error that occurred for `UNION ALL` queries inside a sub-query if one of the `SELECT` queries contains duplicate column names. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2094)
- Fixed a memory leak if an exception occurred when connecting to a MySQL server.
- Fixed incorrect clickhouse-client response code in case of a query error.
- The allocator has been replaced: `jemalloc` is now used instead of `tcmalloc`. In some scenarios, this increases speed up to 20%. However, there are queries that have slowed by up to 20%. Memory consumption has been reduced by approximately 10% in some scenarios, with improved stability. With highly competitive loads, CPU usage in userspace and in system shows just a slight increase. [#2773](https://github.com/ClickHouse/ClickHouse/pull/2773)
- Use of libressl from a submodule. [#1983](https://github.com/ClickHouse/ClickHouse/pull/1983) [#2807](https://github.com/ClickHouse/ClickHouse/pull/2807)
- Use of unixodbc from a submodule. [#2789](https://github.com/ClickHouse/ClickHouse/pull/2789)
- Use of mariadb-connector-c from a submodule. [#2785](https://github.com/ClickHouse/ClickHouse/pull/2785)
The expression must be a chain of equalities joined by the AND operator. Each side of the equality can be an arbitrary expression over the columns of one of the tables. The use of fully qualified column names is supported (`table.name`, `database.table.name`, `table_alias.name`, `subquery_alias.name`) for the right table. [#2742](https://github.com/ClickHouse/ClickHouse/pull/2742)
- HTTPS can be enabled for replication. [#2760](https://github.com/ClickHouse/ClickHouse/pull/2760)
- The server passes the patch component of its version to the client. Data about the patch version component is in `system.processes` and `query_log`. [#2646](https://github.com/ClickHouse/ClickHouse/pull/2646)
- Now you can use the `from_env` [#2741](https://github.com/ClickHouse/ClickHouse/pull/2741) attribute to set values in config files from environment variables.
- Added case-insensitive versions of the `coalesce`, `ifNull`, and `nullIf functions` [#2752](https://github.com/ClickHouse/ClickHouse/pull/2752).
- Added the ability to use a table function instead of a table as an argument of a `remote` or `cluster table function` [#2708](https://github.com/ClickHouse/ClickHouse/pull/2708).
- Support for `HTTP Basic` authentication in the replication protocol [#2727](https://github.com/ClickHouse/ClickHouse/pull/2727).
- The `has` function now allows searching for a numeric value in an array of `Enum` values [Maxim Khrisanfov](https://github.com/ClickHouse/ClickHouse/pull/2699).
- Support for adding arbitrary message separators when reading from `Kafka` [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2701).
- The `ALTER TABLE t DELETE WHERE` query does not rewrite data parts that were not affected by the WHERE condition [#2694](https://github.com/ClickHouse/ClickHouse/pull/2694).
- The `use_minimalistic_checksums_in_zookeeper` option for `ReplicatedMergeTree` tables is enabled by default. This setting was added in version 1.1.54378, 2018-04-16. Versions that are older than 1.1.54378 can no longer be installed.
- Support for running `KILL` and `OPTIMIZE` queries that specify `ON CLUSTER` [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2689).
- Fixed the error `Column ... is not under an aggregate function and not in GROUP BY` for aggregation with an IN expression. This bug appeared in version 18.1.0. ([bbdd780b](https://github.com/ClickHouse/ClickHouse/commit/bbdd780be0be06a0f336775941cdd536878dd2c2))
- Fixed a bug in the `windowFunnel aggregate function` [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2735).
- Fixed a bug in the `anyHeavy` aggregate function ([a2101df2](https://github.com/ClickHouse/ClickHouse/commit/a2101df25a6a0fba99aa71f8793d762af2b801ee))
- Fixed server crash when using the `countArray()` aggregate function.
- Parameters for `Kafka` engine was changed from `Kafka(kafka_broker_list, kafka_topic_list, kafka_group_name, kafka_format[, kafka_schema, kafka_num_consumers])` to `Kafka(kafka_broker_list, kafka_topic_list, kafka_group_name, kafka_format[, kafka_row_delimiter, kafka_schema, kafka_num_consumers])`. If your tables use `kafka_schema` or `kafka_num_consumers` parameters, you have to manually edit the metadata files `path/metadata/database/table.sql` and add `kafka_row_delimiter` parameter with `''` value.
- Support for the `ALTER TABLE t DELETE WHERE` query for non-replicated MergeTree tables ([#2634](https://github.com/ClickHouse/ClickHouse/pull/2634)).
- Support for arbitrary types for the `uniq*` family of aggregate functions ([#2010](https://github.com/ClickHouse/ClickHouse/issues/2010)).
- Support for arbitrary types in comparison operators ([#2026](https://github.com/ClickHouse/ClickHouse/issues/2026)).
- The `users.xml` file allows setting a subnet mask in the format `10.0.0.1/255.255.255.0`. This is necessary for using masks for IPv6 networks with zeros in the middle ([#2637](https://github.com/ClickHouse/ClickHouse/pull/2637)).
- Added the `arrayDistinct` function ([#2670](https://github.com/ClickHouse/ClickHouse/pull/2670)).
- The SummingMergeTree engine can now work with AggregateFunction type columns ([Constantin S. Pan](https://github.com/ClickHouse/ClickHouse/pull/2566)).
- Changed the numbering scheme for release versions. Now the first part contains the year of release (A.D., Moscow timezone, minus 2000), the second part contains the number for major changes (increases for most releases), and the third part is the patch version. Releases are still backward compatible, unless otherwise stated in the changelog.
- Faster conversions of floating-point numbers to a string ([Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2664)).
- If some rows were skipped during an insert due to parsing errors (this is possible with the `input_allow_errors_num` and `input_allow_errors_ratio` settings enabled), the number of skipped rows is now written to the server log ([Leonardo Cecchi](https://github.com/ClickHouse/ClickHouse/pull/2669)).
- Fixed the TRUNCATE command for temporary tables ([Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2624)).
- Fixed a rare deadlock in the ZooKeeper client library that occurred when there was a network error while reading the response ([c315200](https://github.com/ClickHouse/ClickHouse/commit/c315200e64b87e44bdf740707fc857d1fdf7e947)).
- Fixed the incorrect result of the `maxIntersection()` function when the boundaries of intervals coincided ([Michael Furmur](https://github.com/ClickHouse/ClickHouse/pull/2657)).
- Fixed incorrect transformation of the OR expression chain in a function argument ([chenxing-xc](https://github.com/ClickHouse/ClickHouse/pull/2663)).
- Fixed incompatibility between servers with different versions in distributed queries that use a `CAST` function that isn’t in uppercase letters ([fe8c4d6](https://github.com/ClickHouse/ClickHouse/commit/fe8c4d64e434cacd4ceef34faa9005129f2190a5)).
- Converting a string containing the number zero to DateTime does not work. Example: `SELECT toDateTime('0')`. This is also the reason that `DateTime DEFAULT '0'` does not work in tables, as well as `<null_value>0</null_value>` in dictionaries. Solution: replace `0` with `0000-00-00 00:00:00`.
- Added the `histogram` aggregate function ([Mikhail Surin](https://github.com/ClickHouse/ClickHouse/pull/2521)).
- Now `OPTIMIZE TABLE ... FINAL` can be used without specifying partitions for `ReplicatedMergeTree` ([Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2600)).
- Fixed a problem with a very small timeout for sockets (one second) for reading and writing when sending and downloading replicated data, which made it impossible to download larger parts if there is a load on the network or disk (it resulted in cyclical attempts to download parts). This error occurred in version 1.1.54388.
- Fixed issues when using chroot in ZooKeeper if you inserted duplicate data blocks in the table.
- The `system.tables` table now works correctly when used in distributed queries. The `metadata_modification_time` and `engine_full` columns are now non-virtual. Fixed an error that occurred if only these columns were queried from the table.
- Queries can be sent in `multipart/form-data` format (in the `query` field), which is useful if external data is also sent for query processing ([Olga Hvostikova](https://github.com/ClickHouse/ClickHouse/pull/2490)).
- Added the ability to enable or disable processing single or double quotes when reading data in CSV format. You can configure this in the `format_csv_allow_single_quotes` and `format_csv_allow_double_quotes` settings ([Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2574)).
- Now `OPTIMIZE TABLE ... FINAL` can be used without specifying the partition for non-replicated variants of `MergeTree` ([Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2599)).
- Improved performance, reduced memory consumption, and correct memory consumption tracking with use of the IN operator when a table index could be used ([#2584](https://github.com/ClickHouse/ClickHouse/pull/2584)).
- Removed redundant checking of checksums when adding a data part. This is important when there are a large number of replicas, because in these cases the total number of checks was equal to N^2.
- Added support for `Array(Tuple(...))` arguments for the `arrayEnumerateUniq` function ([#2573](https://github.com/ClickHouse/ClickHouse/pull/2573)).
- Added `Nullable` support for the `runningDifference` function ([#2594](https://github.com/ClickHouse/ClickHouse/pull/2594)).
- Improved query analysis performance when there is a very large number of expressions ([#2572](https://github.com/ClickHouse/ClickHouse/pull/2572)).
- Faster selection of data parts for merging in `ReplicatedMergeTree` tables. Faster recovery of the ZooKeeper session ([#2597](https://github.com/ClickHouse/ClickHouse/pull/2597)).
- The `format_version.txt` file for `MergeTree` tables is re-created if it is missing, which makes sense if ClickHouse is launched after copying the directory structure without files ([Ciprian Hacman](https://github.com/ClickHouse/ClickHouse/pull/2593)).
- Fixed a bug when working with ZooKeeper that could make it impossible to recover the session and readonly states of tables before restarting the server.
- Fixed a bug when working with ZooKeeper that could result in old nodes not being deleted if the session is interrupted.
- Fixed an error in the `quantileTDigest` function for Float arguments (this bug was introduced in version 1.1.54388) ([Mikhail Surin](https://github.com/ClickHouse/ClickHouse/pull/2553)).
- Fixed a bug in the index for MergeTree tables if the primary key column is located inside the function for converting types between signed and unsigned integers of the same size ([#2603](https://github.com/ClickHouse/ClickHouse/pull/2603)).
- Fixed segfault if `macros` are used but they aren’t in the config file ([#2570](https://github.com/ClickHouse/ClickHouse/pull/2570)).
- Fixed switching to the default database when reconnecting the client ([#2583](https://github.com/ClickHouse/ClickHouse/pull/2583)).
- Support for the `ALTER TABLE t DELETE WHERE` query for replicated tables. Added the `system.mutations` table to track progress of this type of queries.
- Support for the `ALTER TABLE t [REPLACE|ATTACH] PARTITION` query for \*MergeTree tables.
- Support for the `TRUNCATE TABLE` query ([Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2260))
- Several new `SYSTEM` queries for replicated tables (`RESTART REPLICAS`, `SYNC REPLICA`, `[STOP|START] [MERGES|FETCHES|SENDS REPLICATED|REPLICATION QUEUES]`).
- Added the ability to write to a table with the MySQL engine and the corresponding table function ([sundy-li](https://github.com/ClickHouse/ClickHouse/pull/2294)).
- Added the `url()` table function and the `URL` table engine ([Alexander Sapin](https://github.com/ClickHouse/ClickHouse/pull/2501)).
- Added the `windowFunnel` aggregate function ([sundy-li](https://github.com/ClickHouse/ClickHouse/pull/2352)).
- New `startsWith` and `endsWith` functions for strings ([Vadim Plakhtinsky](https://github.com/ClickHouse/ClickHouse/pull/2429)).
- The `numbers()` table function now allows you to specify the offset ([Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2535)).
- The password to `clickhouse-client` can be entered interactively.
- Server logs can now be sent to syslog ([Alexander Krasheninnikov](https://github.com/ClickHouse/ClickHouse/pull/2459)).
- Support for logging in dictionaries with a shared library source ([Alexander Sapin](https://github.com/ClickHouse/ClickHouse/pull/2472)).
- Support for custom CSV delimiters ([Ivan Zhukov](https://github.com/ClickHouse/ClickHouse/pull/2263))
- Added the `date_time_input_format` setting. If you switch this setting to `'best_effort'`, DateTime values will be read in a wide range of formats.
- Added the `clickhouse-obfuscator` utility for data obfuscation. Usage example: publishing data used in performance tests.
- Fixed an error when reading from ReplacingMergeTree with a condition in PREWHERE that filters all rows ([#2525](https://github.com/ClickHouse/ClickHouse/issues/2525)).
- Type mapping in the ODBC table function has been fixed ([sundy-li](https://github.com/ClickHouse/ClickHouse/pull/2268)).
- Type comparisons have been fixed for `DateTime` with and without the time zone ([Alexander Bocharov](https://github.com/ClickHouse/ClickHouse/pull/2400)).
- Fixed syntactic parsing and formatting of the `CAST` operator.
- Fixed insertion into a materialized view for the Distributed table engine ([Babacar Diassé](https://github.com/ClickHouse/ClickHouse/pull/2411)).
- Fixed a race condition when writing data from the `Kafka` engine to materialized views ([Yangkuan Liu](https://github.com/ClickHouse/ClickHouse/pull/2448)).
- Background tasks in replicated tables are now performed in a thread pool instead of in separate threads ([Silviu Caragea](https://github.com/ClickHouse/ClickHouse/pull/1722)).
- Improved LZ4 compression performance.
- Faster analysis for queries with a large number of JOINs and sub-queries.
- The DNS cache is now updated automatically when there are too many network errors.
- Table inserts no longer occur if the insert into one of the materialized views is not possible because it has too many parts.
- Corrected the discrepancy in the event counters `Query`, `SelectQuery`, and `InsertQuery`.
- Expressions like `tuple IN (SELECT tuple)` are allowed if the tuple types match.
- A server with replicated tables can start even if you haven’t configured ZooKeeper.
- When calculating the number of available CPU cores, limits on cgroups are now taken into account ([Atri Sharma](https://github.com/ClickHouse/ClickHouse/pull/2325)).
- Added chown for config directories in the systemd config file ([Mikhail Shiryaev](https://github.com/ClickHouse/ClickHouse/pull/2421)).
- Removed escaping in `Vertical` and `Pretty*` formats and deleted the `VerticalRaw` format.
- If servers with version 1.1.54388 (or newer) and servers with an older version are used simultaneously in a distributed query and the query has the `cast(x, 'Type')` expression without the `AS` keyword and doesn’t have the word `cast` in uppercase, an exception will be thrown with a message like `Not found column cast(0, 'UInt8') in block`. Solution: Update the server on the entire cluster.
- Added the table function `file(path, format, structure)`. An example reading bytes from `/dev/urandom`: ``` ln -s /dev/urandom /var/lib/clickhouse/user_files/random``clickhouse-client -q "SELECT * FROM file('random', 'RowBinary', 'd UInt8') LIMIT 10" ```.
- Fixed incorrect behavior of the `IN` operator when select from `MATERIALIZED VIEW`.
- Fixed incorrect filtering by partition index in expressions like `partition_key_column IN (...)`.
- Fixed inability to execute `OPTIMIZE` query on non-leader replica if `REANAME` was performed on the table.
- Fixed the authorization error when executing `OPTIMIZE` or `ALTER` queries on a non-leader replica.
- Fixed freezing of `KILL QUERY`.
- Fixed an error in ZooKeeper client library which led to loss of watches, freezing of distributed DDL queue, and slowdowns in the replication queue if a non-empty `chroot` prefix is used in the ZooKeeper configuration.
- Removed support for expressions like `(a, b) IN (SELECT (a, b))` (you can use the equivalent expression `(a, b) IN (SELECT a, b)`). In previous releases, these expressions led to undetermined `WHERE` filtering or caused errors.
- Logging level can be changed without restarting the server.
- Added the `SHOW CREATE DATABASE` query.
- The `query_id` can be passed to `clickhouse-client` (elBroom).
- New setting: `max_network_bandwidth_for_all_users`.
- Added support for `ALTER TABLE ... PARTITION ...` for `MATERIALIZED VIEW`.
- Added information about the size of data parts in uncompressed form in the system table.
- Server-to-server encryption support for distributed tables (`<secure>1</secure>` in the replica config in `<remote_servers>`).
- Configuration of the table level for the `ReplicatedMergeTree` family in order to minimize the amount of data stored in Zookeeper: : `use_minimalistic_checksums_in_zookeeper = 1`
- Configuration of the `clickhouse-client` prompt. By default, server names are now output to the prompt. The server’s display name can be changed. It’s also sent in the `X-ClickHouse-Display-Name` HTTP header (Kirill Shvakov).
- Multiple comma-separated `topics` can be specified for the `Kafka` engine (Tobias Adamson)
- When a query is stopped by `KILL QUERY` or `replace_running_query`, the client receives the `Query was canceled` exception instead of an incomplete result.
-`ALTER TABLE ... DROP/DETACH PARTITION` queries are run at the front of the replication queue.
-`SELECT ... FINAL` and `OPTIMIZE ... FINAL` can be used even when the table has a single data part.
- A `query_log` table is recreated on the fly if it was deleted manually (Kirill Shvakov).
- The `lengthUTF8` function runs faster (zhang2014).
- Improved performance of synchronous inserts in `Distributed` tables (`insert_distributed_sync = 1`) when there is a very large number of shards.
- The server accepts the `send_timeout` and `receive_timeout` settings from the client and applies them when connecting to the client (they are applied in reverse order: the server socket’s `send_timeout` is set to the `receive_timeout` value received from the client, and vice versa).
- More robust crash recovery for asynchronous insertion into `Distributed` tables.
- The return type of the `countEqual` function changed from `UInt32` to `UInt64` (谢磊).
- The build supports `ninja` instead of `make` and uses `ninja` by default for building releases.
- Renamed packages: `clickhouse-server-base` in `clickhouse-common-static`; `clickhouse-server-common` in `clickhouse-server`; `clickhouse-common-dbg` in `clickhouse-common-static-dbg`. To install, use `clickhouse-server clickhouse-client`. Packages with the old names will still load in the repositories for backward compatibility.
- Removed the special interpretation of an IN expression if an array is specified on the left side. Previously, the expression `arr IN (set)` was interpreted as “at least one `arr` element belongs to the `set`”. To get the same behavior in the new version, write `arrayExists(x -> x IN (set), arr)`.
- Disabled the incorrect use of the socket option `SO_REUSEPORT`, which was incorrectly enabled by default in the Poco library. Note that on Linux there is no longer any reason to simultaneously specify the addresses `::` and `0.0.0.0` for listen – use just `::`, which allows listening to the connection both over IPv4 and IPv6 (with the default kernel config settings). You can also revert to the behavior from previous versions by specifying `<listen_reuse_port>1</listen_reuse_port>` in the config.
- Added the `system.macros` table and auto updating of macros when the config file is changed.
- Added the `SYSTEM RELOAD CONFIG` query.
- Added the `maxIntersections(left_col, right_col)` aggregate function, which returns the maximum number of simultaneously intersecting intervals `[left; right]`. The `maxIntersectionsPosition(left, right)` function returns the beginning of the “maximum” interval. ([Michael Furmur](https://github.com/ClickHouse/ClickHouse/pull/2012)).
- When inserting data in a `Replicated` table, fewer requests are made to `ZooKeeper` (and most of the user-level errors have disappeared from the `ZooKeeper` log).
- Added the ability to create aliases for data sets. Example: `WITH (1, 2, 3) AS set SELECT number IN set FROM system.numbers LIMIT 10`.
- Fixed the `Illegal PREWHERE` error when reading from Merge tables for `Distributed`tables.
- Added fixes that allow you to start clickhouse-server in IPv4-only Docker containers.
- Fixed a race condition when reading from system `system.parts_columns tables.`
- Removed double buffering during a synchronous insert to a `Distributed` table, which could have caused the connection to timeout.
- Fixed a bug that caused excessively long waits for an unavailable replica before beginning a `SELECT` query.
- Fixed incorrect dates in the `system.parts` table.
- Fixed a bug that made it impossible to insert data in a `Replicated` table if `chroot` was non-empty in the configuration of the `ZooKeeper` cluster.
- Fixed the vertical merging algorithm for an empty `ORDER BY` table.
- Restored the ability to use dictionaries in queries to remote tables, even if these dictionaries are not present on the requestor server. This functionality was lost in release 1.1.54362.
- Restored the behavior for queries like `SELECT * FROM remote('server2', default.table) WHERE col IN (SELECT col2 FROM default.table)` when the right side of the `IN` should use a remote `default.table` instead of a local one. This behavior was broken in version 1.1.54358.
- Removed extraneous error-level logging of `Not found column ... in block`.
- Aggregation without `GROUP BY` for an empty set (such as `SELECT count(*) FROM table WHERE 0`) now returns a result with one row with null values for aggregate functions, in compliance with the SQL standard. To restore the old behavior (return an empty result), set `empty_result_for_aggregation_by_empty_set` to 1.
- Added type conversion for `UNION ALL`. Different alias names are allowed in `SELECT` positions in `UNION ALL`, in compliance with the SQL standard.
- Arbitrary expressions are supported in `LIMIT BY` clauses. Previously, it was only possible to use columns resulting from `SELECT`.
- An index of `MergeTree` tables is used when `IN` is applied to a tuple of expressions from the columns of the primary key. Example: `WHERE (UserID, EventDate) IN ((123, '2000-01-01'), ...)` (Anastasiya Tsarkova).
- Added the `clickhouse-copier` tool for copying between clusters and resharding data (beta).
- Added consistent hashing functions: `yandexConsistentHash`, `jumpConsistentHash`, `sumburConsistentHash`. They can be used as a sharding key in order to reduce the amount of network traffic during subsequent reshardings.
- Added the `arrayCumSum` function (Javi Santana).
- Added the `parseDateTimeBestEffort`, `parseDateTimeBestEffortOrZero`, and `parseDateTimeBestEffortOrNull` functions to read the DateTime from a string containing text in a wide variety of possible formats.
- Data can be partially reloaded from external dictionaries during updating (load just the records in which the value of the specified field greater than in the previous download) (Arsen Hakobyan).
- Added the `cluster` table function. Example: `cluster(cluster_name, db, table)`. The `remote` table function can accept the cluster name as the first argument, if it is specified as an identifier.
- The `remote` and `cluster` table functions can be used in `INSERT` queries.
- Added the `create_table_query` and `engine_full` virtual columns to the `system.tables`table . The `metadata_modification_time` column is virtual.
- Added the `data_path` and `metadata_path` columns to `system.tables`and`system.databases` tables, and added the `path` column to the `system.parts` and `system.parts_columns` tables.
- Added additional information about merges in the `system.part_log` table.
- An arbitrary partitioning key can be used for the `system.query_log` table (Kirill Shvakov).
- The `SHOW TABLES` query now also shows temporary tables. Added temporary tables and the `is_temporary` column to `system.tables` (zhang2014).
- Support for `SHOW CREATE TABLE` for temporary tables (zhang2014).
- Added the `system_profile` configuration parameter for the settings used by internal processes.
- Support for loading `object_id` as an attribute in `MongoDB` dictionaries (Pavel Litvinenko).
- Reading `null` as the default value when loading data for an external dictionary with the `MongoDB` source (Pavel Litvinenko).
- Reading `DateTime` values in the `Values` format from a Unix timestamp without single quotes.
- Failover is supported in `remote` table functions for cases when some of the replicas are missing the requested table.
- Configuration settings can be overridden in the command line when you run `clickhouse-server`. Example: `clickhouse-server -- --logger.level=information`.
- Implemented the `empty` function from a `FixedString` argument: the function returns 1 if the string consists entirely of null bytes (zhang2014).
- Added the `listen_try`configuration parameter for listening to at least one of the listen addresses without quitting, if some of the addresses can’t be listened to (useful for systems with disabled support for IPv4 or IPv6).
- Added the `VersionedCollapsingMergeTree` table engine.
- Support for rows and arbitrary numeric types for the `library` dictionary source.
-`MergeTree` tables can be used without a primary key (you need to specify `ORDER BY tuple()`).
- A `Nullable` type can be `CAST` to a non-`Nullable` type if the argument is not `NULL`.
-`RENAME TABLE` can be performed for `VIEW`.
- Added the `throwIf` function.
- Added the `odbc_default_field_size` option, which allows you to extend the maximum size of the value loaded from an ODBC source (by default, it is 1024).
- The `system.processes` table and `SHOW PROCESSLIST` now have the `is_cancelled` and `peak_memory_usage` columns.
- Limits and quotas on the result are no longer applied to intermediate data for `INSERT SELECT` queries or for `SELECT` subqueries.
- Fewer false triggers of `force_restore_data` when checking the status of `Replicated` tables when the server starts.
- Added the `allow_distributed_ddl` option.
- Nondeterministic functions are not allowed in expressions for `MergeTree` table keys.
- Files with substitutions from `config.d` directories are loaded in alphabetical order.
- Improved performance of the `arrayElement` function in the case of a constant multidimensional array with an empty array as one of the elements. Example: `[[1], []][x]`.
- The server starts faster now when using configuration files with very large substitutions (for instance, very large lists of IP networks).
- When running a query, table valued functions run once. Previously, `remote` and `mysql` table valued functions performed the same query twice to retrieve the table structure from a remote server.
- The `MkDocs` documentation generator is used.
- When you try to delete a table column that `DEFAULT`/`MATERIALIZED` expressions of other columns depend on, an exception is thrown (zhang2014).
- Added the ability to parse an empty line in text formats as the number 0 for `Float` data types. This feature was previously available but was lost in release 1.1.54342.
-`Enum` values can be used in `min`, `max`, `sum` and some other functions. In these cases, it uses the corresponding numeric values. This feature was previously available but was lost in the release 1.1.54337.
- Added `max_expanded_ast_elements` to restrict the size of the AST after recursively expanding aliases.
- Fixed cases when unnecessary columns were removed from subqueries in error, or not removed from subqueries containing `UNION ALL`.
- Fixed a bug in merges for `ReplacingMergeTree` tables.
- Fixed synchronous insertions in `Distributed` tables (`insert_distributed_sync = 1`).
- Fixed segfault for certain uses of `FULL` and `RIGHT JOIN` with duplicate columns in subqueries.
- Fixed segfault for certain uses of `replace_running_query` and `KILL QUERY`.
- Fixed the order of the `source` and `last_exception` columns in the `system.dictionaries` table.
- Fixed a bug when the `DROP DATABASE` query did not delete the file with metadata.
- Fixed the `DROP DATABASE` query for `Dictionary` databases.
- Fixed the low precision of `uniqHLL12` and `uniqCombined` functions for cardinalities greater than 100 million items (Alex Bocharov).
- Fixed the calculation of implicit default values when necessary to simultaneously calculate default explicit expressions in `INSERT` queries (zhang2014).
- Fixed a rare case when a query to a `MergeTree` table couldn’t finish (chenxing-xc).
- Fixed a crash that occurred when running a `CHECK` query for `Distributed` tables if all shards are local (chenxing.xc).
- Fixed a slight performance regression with functions that use regular expressions.
- Fixed a performance regression when creating multidimensional arrays from complex expressions.
- Fixed a bug that could cause an extra `FORMAT` section to appear in an `.sql` file with metadata.
- Fixed a bug that caused the `max_table_size_to_drop` limit to apply when trying to delete a `MATERIALIZED VIEW` looking at an explicitly specified table.
- Fixed incompatibility with old clients (old clients were sometimes sent data with the `DateTime('timezone')` type, which they do not understand).
- Fixed a bug when reading `Nested` column elements of structures that were added using `ALTER` but that are empty for the old partitions, when the conditions for these columns moved to `PREWHERE`.
- Fixed a bug when filtering tables by virtual `_table` columns in queries to `Merge` tables.
- Fixed a bug when using `ALIAS` columns in `Distributed` tables.
- Fixed a bug that made dynamic compilation impossible for queries with aggregate functions from the `quantile` family.
- Fixed a race condition in the query execution pipeline that occurred in very rare cases when using `Merge` tables with a large number of tables, and when using `GLOBAL` subqueries.
- Fixed a crash when passing arrays of different sizes to an `arrayReduce` function when using aggregate functions from multiple arguments.
- Prohibited the use of queries with `UNION ALL` in a `MATERIALIZED VIEW`.
- Fixed an error during initialization of the `part_log` system table when the server starts (by default, `part_log` is disabled).
- Added macros support for defining cluster names in distributed DDL queries and constructors of Distributed tables: `CREATE TABLE distr ON CLUSTER '{cluster}' (...) ENGINE = Distributed('{cluster}', 'db', 'table')`.
- Now queries like `SELECT ... FROM table WHERE expr IN (subquery)` are processed using the `table` index.
- Improved processing of duplicates when inserting to Replicated tables, so they no longer slow down execution of the replication queue.
- Fixed a regression in 1.1.54337: if the default user has readonly access, then the server refuses to start up with the message `Cannot create database in readonly mode`.
- Fixed a regression in 1.1.54337: on systems with systemd, logs are always written to syslog regardless of the configuration; the watchdog script still uses init.d.
- Fixed a regression in 1.1.54337: wrong default configuration in the Docker image.
- Fixed nondeterministic behavior of GraphiteMergeTree (you can see it in log messages `Data after merge is not byte-identical to the data on another replicas`).
- Fixed a bug that may lead to inconsistent merges after OPTIMIZE query to Replicated tables (you may see it in log messages `Part ... intersects the previous part`).
- Buffer tables now work correctly when MATERIALIZED columns are present in the destination table (by zhang2014).
- Added support for storage of multi-dimensional arrays and tuples (`Tuple` data type) in tables.
- Support for table functions for `DESCRIBE` and `INSERT` queries. Added support for subqueries in `DESCRIBE`. Examples: `DESC TABLE remote('host', default.hits)`; `DESC TABLE (SELECT 1)`; `INSERT INTO TABLE FUNCTION remote('host', default.hits)`. Support for `INSERT INTO TABLE` in addition to `INSERT INTO`.
- Improved support for time zones. The `DateTime` data type can be annotated with the timezone that is used for parsing and formatting in text formats. Example: `DateTime('Europe/Moscow')`. When timezones are specified in functions for `DateTime` arguments, the return type will track the timezone, and the value will be displayed as expected.
- Added the functions `toTimeZone`, `timeDiff`, `toQuarter`, `toRelativeQuarterNum`. The `toRelativeHour`/`Minute`/`Second` functions can take a value of type `Date` as an argument. The `now` function name is case-sensitive.
- Added the `toStartOfFifteenMinutes` function (Kirill Shvakov).
- Added the `clickhouse format` tool for formatting queries.
- Added the `format_schema_path` configuration parameter (Marek Vavruşa). It is used for specifying a schema in `Cap'n Proto` format. Schema files can be located only in the specified directory.
- Added support for config substitutions (`incl` and `conf.d`) for configuration of external dictionaries and models (Pavel Yakunin).
- Added a column with documentation for the `system.settings` table (Kirill Shvakov).
- Added the `system.parts_columns` table with information about column sizes in each data part of `MergeTree` tables.
- Added the `system.models` table with information about loaded `CatBoost` machine learning models.
- Added the `mysql` and `odbc` table function and corresponding `MySQL` and `ODBC` table engines for accessing remote databases. This functionality is in the beta stage.
- Added the possibility to pass an argument of type `AggregateFunction` for the `groupArray` aggregate function (so you can create an array of states of some aggregate function).
- Removed restrictions on various combinations of aggregate function combinators. For example, you can use `avgForEachIf` as well as `avgIfForEach` aggregate functions, which have different behaviors.
- The `-ForEach` aggregate function combinator is extended for the case of aggregate functions of multiple arguments.
- Added support for aggregate functions of `Nullable` arguments even for cases when the function returns a non-`Nullable` result (added with the contribution of Silviu Caragea). Example: `groupArray`, `groupUniqArray`, `topK`.
- Added the `max_client_network_bandwidth` for `clickhouse-client` (Kirill Shvakov).
- Users with the `readonly = 2` setting are allowed to work with TEMPORARY tables (CREATE, DROP, INSERT…) (Kirill Shvakov).
- Added support for using multiple consumers with the `Kafka` engine. Extended configuration options for `Kafka` (Marek Vavruša).
- Added the `intExp3` and `intExp4` functions.
- Added the `sumKahan` aggregate function.
- Added the to \* Number\* OrNull functions, where \* Number\* is a numeric type.
- Added support for `WITH` clauses for an `INSERT SELECT` query (author: zhang2014).
- Added settings: `http_connection_timeout`, `http_send_timeout`, `http_receive_timeout`. In particular, these settings are used for downloading data parts for replication. Changing these settings allows for faster failover if the network is overloaded.
- Added support for `ALTER` for tables of type `Null` (Anastasiya Tsarkova).
- The `reinterpretAsString` function is extended for all data types that are stored contiguously in memory.
- Added the `--silent` option for the `clickhouse-local` tool. It suppresses printing query execution info in stderr.
- Added support for reading values of type `Date` from text in a format where the month and/or day of the month is specified using a single digit instead of two digits (Amos Bird).
- Improved performance of aggregate functions `min`, `max`, `any`, `anyLast`, `anyHeavy`, `argMin`, `argMax` from string arguments.
- Improved performance of the functions `isInfinite`, `isFinite`, `isNaN`, `roundToExp2`.
- Improved performance of parsing and formatting `Date` and `DateTime` type values in text format.
- Improved performance and precision of parsing floating point numbers.
- Lowered memory usage for `JOIN` in the case when the left and right parts have columns with identical names that are not contained in `USING` .
- Improved performance of aggregate functions `varSamp`, `varPop`, `stddevSamp`, `stddevPop`, `covarSamp`, `covarPop`, `corr` by reducing computational stability. The old functions are available under the names `varSampStable`, `varPopStable`, `stddevSampStable`, `stddevPopStable`, `covarSampStable`, `covarPopStable`, `corrStable`.
- Fixed data deduplication after running a `DROP` or `DETACH PARTITION` query. In the previous version, dropping a partition and inserting the same data again was not working because inserted blocks were considered duplicates.
- Fixed a bug that could lead to incorrect interpretation of the `WHERE` clause for `CREATE MATERIALIZED VIEW` queries with `POPULATE` .
- Fixed a bug in using the `root_path` parameter in the `zookeeper_servers` configuration.
- Fixed unexpected results of passing the `Date` argument to `toStartOfDay` .
- Fixed the `addMonths` and `subtractMonths` functions and the arithmetic for `INTERVAL n MONTH` in cases when the result has the previous year.
- Added missing support for the `UUID` data type for `DISTINCT` , `JOIN` , and `uniq` aggregate functions and external dictionaries (Evgeniy Ivanov). Support for `UUID` is still incomplete.
- Fixed `SummingMergeTree` behavior in cases when the rows summed to zero.
- Various fixes for the `Kafka` engine (Marek Vavruša).
- Fixed incorrect behavior of the `Join` table engine (Amos Bird).
- Fixed incorrect allocator behavior under FreeBSD and OS X.
- The `extractAll` function now supports empty matches.
- Fixed an error that blocked usage of `libressl` instead of `openssl` .
- Fixed the `CREATE TABLE AS SELECT` query from temporary tables.
- Fixed non-atomicity of updating the replication queue. This could lead to replicas being out of sync until the server restarts.
- Fixed possible overflow in `gcd` , `lcm` and `modulo` (`%` operator) (Maks Skorokhod).
-`-preprocessed` files are now created after changing `umask` (`umask` can be changed in the config).
- Fixed a bug in the background check of parts (`MergeTreePartChecker` ) when using a custom partition key.
- Fixed parsing of tuples (values of the `Tuple` data type) in text formats.
- Improved error messages about incompatible types passed to `multiIf` , `array` and some other functions.
- Redesigned support for `Nullable` types. Fixed bugs that may lead to a server crash. Fixed almost all other bugs related to `NULL` support: incorrect type conversions in INSERT SELECT, insufficient support for Nullable in HAVING and PREWHERE, `join_use_nulls` mode, Nullable types as arguments of `OR` operator, etc.
- Fixed various bugs related to internal semantics of data types. Examples: unnecessary summing of `Enum` type fields in `SummingMergeTree` ; alignment of `Enum` types in `Pretty` formats, etc.
- Stricter checks for allowed combinations of composite columns.
- Fixed the overflow when specifying a very large parameter for the `FixedString` data type.
- Fixed a bug in the `topK` aggregate function in a generic case.
- Added the missing check for equality of array sizes in arguments of n-ary variants of aggregate functions with an `-Array` combinator.
- Fixed a bug in `--pager` for `clickhouse-client` (author: ks1322).
- Fixed the precision of the `exp10` function.
- Fixed the behavior of the `visitParamExtract` function for better compliance with documentation.
- Fixed the crash when incorrect data types are specified.
- Fixed the behavior of `DISTINCT` in the case when all columns are constants.
- Fixed query formatting in the case of using the `tupleElement` function with a complex constant expression as the tuple element index.
- Fixed a bug in `Dictionary` tables for `range_hashed` dictionaries.
- Fixed a bug that leads to excessive rows in the result of `FULL` and `RIGHT JOIN` (Amos Bird).
- Fixed a server crash when creating and removing temporary files in `config.d` directories during config reload.
- Fixed the `SYSTEM DROP DNS CACHE` query: the cache was flushed but addresses of cluster nodes were not updated.
- Fixed the behavior of `MATERIALIZED VIEW` after executing `DETACH TABLE` for the table under the view (Marek Vavruša).
- The `pbuilder` tool is used for builds. The build process is almost completely independent of the build host environment.
- A single build is used for different OS versions. Packages and binaries have been made compatible with a wide range of Linux systems.
- Added the `clickhouse-test` package. It can be used to run functional tests.
- The source tarball can now be published to the repository. It can be used to reproduce the build without using GitHub.
- Added limited integration with Travis CI. Due to limits on build time in Travis, only the debug build is tested and a limited subset of tests are run.
- Added support for `Cap'n'Proto` in the default build.
- Changed the format of documentation sources from `Restricted Text` to `Markdown`.
- Added support for `systemd` (Vladimir Smirnov). It is disabled by default due to incompatibility with some OS images and can be enabled manually.
- For dynamic code generation, `clang` and `lld` are embedded into the `clickhouse` binary. They can also be invoked as `clickhouse clang` and `clickhouse lld` .
- Removed usage of GNU extensions from the code. Enabled the `-Wextra` option. When building with `clang` the default is `libc++` instead of `libstdc++`.
- Extracted `clickhouse_parsers` and `clickhouse_common_io` libraries to speed up builds of various tools.
- The format for marks in `Log` type tables that contain `Nullable` columns was changed in a backward incompatible way. If you have these tables, you should convert them to the `TinyLog` type before starting up the new server version. To do this, replace `ENGINE = Log` with `ENGINE = TinyLog` in the corresponding `.sql` file in the `metadata` directory. If your table doesn’t have `Nullable` columns or if the type of your table is not `Log`, then you don’t need to do anything.
- Removed the `experimental_allow_extended_storage_definition_syntax` setting. Now this feature is enabled by default.
- The `runningIncome` function was renamed to `runningDifferenceStartingWithFirstvalue` to avoid confusion.
- Removed the `FROM ARRAY JOIN arr` syntax when ARRAY JOIN is specified directly after FROM with no table (Amos Bird).
- Removed the `BlockTabSeparated` format that was used solely for demonstration purposes.
- Changed the state format for aggregate functions `varSamp`, `varPop`, `stddevSamp`, `stddevPop`, `covarSamp`, `covarPop`, `corr`. If you have stored states of these aggregate functions in tables (using the `AggregateFunction` data type or materialized views with corresponding states), please write to clickhouse-feedback@yandex-team.com.
- In previous server versions there was an undocumented feature: if an aggregate function depends on parameters, you can still specify it without parameters in the AggregateFunction data type. Example: `AggregateFunction(quantiles, UInt64)` instead of `AggregateFunction(quantiles(0.5, 0.9), UInt64)`. This feature was lost. Although it was undocumented, we plan to support it again in future releases.
- Enum data types cannot be used in min/max aggregate functions. This ability will be returned in the next release.
- When doing a rolling update on a cluster, at the point when some of the replicas are running the old version of ClickHouse and some are running the new version, replication is temporarily stopped and the message `unknown parameter 'shard'` appears in the log. Replication will continue after all replicas of the cluster are updated.
- If different versions of ClickHouse are running on the cluster servers, it is possible that distributed queries using the following functions will have incorrect results: `varSamp`, `varPop`, `stddevSamp`, `stddevPop`, `covarSamp`, `covarPop`, `corr`. You should update all cluster nodes.
