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Create information_schema

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Задокументировал information_schema.
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Dmitriy 2021-10-21 22:41:11 +03:00
parent 3eed1f06ea
commit 6725dc2a16
5 changed files with 158 additions and 20 deletions
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31
docs/en/operations/system-tables/columns.md
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@ -24,6 +24,11 @@ Columns:
- `is_in_primary_key` ([UInt8](../../sql-reference/data-types/int-uint.md)) — Flag that indicates whether the column is in the primary key expression.
- `is_in_sampling_key` ([UInt8](../../sql-reference/data-types/int-uint.md)) — Flag that indicates whether the column is in the sampling key expression.
- `compression_codec` ([String](../../sql-reference/data-types/string.md)) — Compression codec name.
- `character_octet_length` ([Nullable](../../sql-reference/data-types/nullable.md)([UInt64](../../sql-reference/data-types/int-uint.md))) — Maximum length in bytes for binary data, character data, or text data and images.
- `numeric_precision` ([Nullable](../../sql-reference/data-types/nullable.md)([UInt64](../../sql-reference/data-types/int-uint.md))) — Accuracy of approximate numeric data, exact numeric data, integer data, or monetary data. Otherwise, the NULL value is returned.
- `numeric_precision_radix` ([Nullable](../../sql-reference/data-types/nullable.md)([UInt64](../../sql-reference/data-types/int-uint.md))) — The base of the number system is the accuracy of approximate numeric data, exact numeric data, integer data or monetary data. Otherwise, the NULL value is returned.
- `numeric_scale` ([Nullable](../../sql-reference/data-types/nullable.md)([UInt64](../../sql-reference/data-types/int-uint.md))) — The scale of approximate numeric data, exact numeric data, integer data, or monetary data. Otherwise, the NULL value is returned.
- `datetime_precision` ([Nullable](../../sql-reference/data-types/nullable.md)([UInt64](../../sql-reference/data-types/int-uint.md))) — Subtype code for `DateTime` and `ISO` interval data types. For other data types, the NULL value is returned.
**Example**
@ -34,10 +39,11 @@ SELECT * FROM system.columns LIMIT 2 FORMAT Vertical;
```text
Row 1:
──────
database: system
table: aggregate_function_combinators
name: name
database: INFORMATION_SCHEMA
table: COLUMNS
name: table_catalog
type: String
position: 1
default_kind:
default_expression:
data_compressed_bytes: 0
@ -49,13 +55,19 @@ is_in_sorting_key: 0
is_in_primary_key: 0
is_in_sampling_key: 0
compression_codec:
character_octet_length: ᴺᵁᴸᴸ
numeric_precision: ᴺᵁᴸᴸ
numeric_precision_radix: ᴺᵁᴸᴸ
numeric_scale: ᴺᵁᴸᴸ
datetime_precision: ᴺᵁᴸᴸ
Row 2:
──────
database: system
table: aggregate_function_combinators
name: is_internal
type: UInt8
database: INFORMATION_SCHEMA
table: COLUMNS
name: table_schema
type: String
position: 2
default_kind:
default_expression:
data_compressed_bytes: 0
@ -67,6 +79,11 @@ is_in_sorting_key: 0
is_in_primary_key: 0
is_in_sampling_key: 0
compression_codec:
character_octet_length: ᴺᵁᴸᴸ
numeric_precision: ᴺᵁᴸᴸ
numeric_precision_radix: ᴺᵁᴸᴸ
numeric_scale: ᴺᵁᴸᴸ
datetime_precision: ᴺᵁᴸᴸ
```
The `system.columns` table contains the following columns (the column type is shown in brackets):

19
docs/en/operations/system-tables/databases.md
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@ -9,6 +9,7 @@ Columns:
- `data_path` ([String](../../sql-reference/data-types/string.md)) — Data path.
- `metadata_path` ([String](../../sql-reference/data-types/enum.md)) — Metadata path.
- `uuid` ([UUID](../../sql-reference/data-types/uuid.md)) — Database UUID.
- `comment` ([String](../../sql-reference/data-types/enum.md)) — Database comment.
The `name` column from this system table is used for implementing the `SHOW DATABASES` query.
@ -17,22 +18,20 @@ The `name` column from this system table is used for implementing the `SHOW DATA
Create a database.
``` sql
CREATE DATABASE test
CREATE DATABASE test;
```
Check all of the available databases to the user.
``` sql
SELECT * FROM system.databases
SELECT * FROM system.databases;
```
``` text
┌─name───────────────────────────┬─engine─┬─data_path──────────────────┬─metadata_path───────────────────────────────────────────────────────┬─────────────────────────────────uuid─┐
│ _temporary_and_external_tables │ Memory │ /var/lib/clickhouse/ │ │ 00000000-0000-0000-0000-000000000000 │
│ default │ Atomic │ /var/lib/clickhouse/store/ │ /var/lib/clickhouse/store/d31/d317b4bd-3595-4386-81ee-c2334694128a/ │ d317b4bd-3595-4386-81ee-c2334694128a │
│ test │ Atomic │ /var/lib/clickhouse/store/ │ /var/lib/clickhouse/store/39b/39bf0cc5-4c06-4717-87fe-c75ff3bd8ebb/ │ 39bf0cc5-4c06-4717-87fe-c75ff3bd8ebb │
│ system │ Atomic │ /var/lib/clickhouse/store/ │ /var/lib/clickhouse/store/1d1/1d1c869d-e465-4b1b-a51f-be033436ebf9/ │ 1d1c869d-e465-4b1b-a51f-be033436ebf9 │
└────────────────────────────────┴────────┴────────────────────────────┴─────────────────────────────────────────────────────────────────────┴──────────────────────────────────────┘
┌─name───────────────┬─engine─┬─data_path──────────────────┬─metadata_path───────────────────────────────────────────────────────┬─uuid─────────────────────────────────┬─comment─┐
│ INFORMATION_SCHEMA │ Memory │ /var/lib/clickhouse/ │ │ 00000000-0000-0000-0000-000000000000 │ │
│ default │ Atomic │ /var/lib/clickhouse/store/ │ /var/lib/clickhouse/store/d31/d317b4bd-3595-4386-81ee-c2334694128a/ │ 24363899-31d7-42a0-a436-389931d752a0 │ │
│ information_schema │ Memory │ /var/lib/clickhouse/ │ │ 00000000-0000-0000-0000-000000000000 │ │
│ system │ Atomic │ /var/lib/clickhouse/store/ │ /var/lib/clickhouse/store/1d1/1d1c869d-e465-4b1b-a51f-be033436ebf9/ │ 03e9f3d1-cc88-4a49-83e9-f3d1cc881a49 │ │
└────────────────────┴────────┴────────────────────────────┴─────────────────────────────────────────────────────────────────────┴──────────────────────────────────────┴─────────┘
```
[Original article](https://clickhouse.tech/docs/en/operations/system-tables/databases) <!--hide-->

117
docs/en/operations/system-tables/information_schema.md Normal file
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@ -0,0 +1,117 @@
# information_schema {#information-schema}
`INFORMATION_SCHEMA` (`information_schema`) is a system database that contains views. Using these views, you can get information about the metadata of database objects.
The structure and composition of system tables may change in different versions of the product, but the support of the `information_schema` makes it possible to change the structure of system tables without changing the method of access to metadata. Metadata requests do not depend on the DBMS used.
``` sql
SHOW TABLES FROM INFORMATION_SCHEMA;
```
``` text
┌─name─────┐
│ COLUMNS │
│ SCHEMATA │
│ TABLES │
│ VIEWS │
└──────────┘
```
`INFORMATION_SCHEMA` contains the following views:
- `SCHEMATA` — The view that can be used to get all the current database schemas.
``` sql
SELECT * FROM information_schema.schemata WHERE schema_name ILIKE 'information_schema' LIMIT 1 FORMAT Vertical;
```
``` text
Row 1:
──────
catalog_name: INFORMATION_SCHEMA
schema_name: INFORMATION_SCHEMA
schema_owner: default
default_character_set_catalog: ᴺᵁᴸᴸ
default_character_set_schema: ᴺᵁᴸᴸ
default_character_set_name: ᴺᵁᴸᴸ
sql_path: ᴺᵁᴸᴸ
```
- `TABLES` — The view that can be used to get all tables in the current database.
``` sql
SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE (table_schema = currentDatabase() OR table_schema = '') AND table_name NOT LIKE '%inner%' LIMIT 1 FORMAT Vertical;
```
``` text
Row 1:
──────
table_catalog: default
table_schema: default
table_name: describe_example
table_type: BASE TABLE
```
- `COLUMNS` — The view that can be used to get a list of table columns in the current database.
``` sql
SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE (table_schema=currentDatabase() OR table_schema='') AND table_name NOT LIKE '%inner%' LIMIT 1 FORMAT Vertical;
```
``` text
Row 1:
──────
table_catalog: default
table_schema: default
table_name: describe_example
column_name: id
ordinal_position: 1
column_default:
is_nullable: 0
data_type: UInt64
character_maximum_length: ᴺᵁᴸᴸ
character_octet_length: ᴺᵁᴸᴸ
numeric_precision: 64
numeric_precision_radix: 2
numeric_scale: 0
datetime_precision: ᴺᵁᴸᴸ
character_set_catalog: ᴺᵁᴸᴸ
character_set_schema: ᴺᵁᴸᴸ
character_set_name: ᴺᵁᴸᴸ
collation_catalog: ᴺᵁᴸᴸ
collation_schema: ᴺᵁᴸᴸ
collation_name: ᴺᵁᴸᴸ
domain_catalog: ᴺᵁᴸᴸ
domain_schema: ᴺᵁᴸᴸ
domain_name: ᴺᵁᴸᴸ
```
- `VIEWS` — The view that can be used to get a list of all views in the current database.
``` sql
CREATE VIEW v (n Nullable(Int32), f Float64) AS SELECT n, f FROM t;
CREATE MATERIALIZED VIEW mv ENGINE = Null AS SELECT * FROM system.one;
SELECT * FROM information_schema.views WHERE table_schema = currentDatabase();
```
``` text
Row 1:
──────
table_catalog: default
table_schema: default
table_name: mv
view_definition: SELECT * FROM system.one
check_option: NONE
is_updatable: NO
is_insertable_into: YES
is_trigger_updatable: NO
is_trigger_deletable: NO
is_trigger_insertable_into: NO
```
**See Also**
- [View](../../sql-reference/statements/create/view.md).
- [system.tables](../../operations/system-tables/tables.md).
- [system.columns](../../operations/system-tables/columns.md).
- [system.views](../../operations/system-tables/views.md).

9
docs/en/operations/system-tables/tables.md
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@ -30,6 +30,8 @@ Columns:
- `engine_full` ([String](../../sql-reference/data-types/string.md)) - Parameters of the table engine.
- `as_select` ([String](../../sql-reference/data-types/string.md)) - `SELECT` query for view.
- `partition_key` ([String](../../sql-reference/data-types/string.md)) - The partition key expression specified in the table.
- `sorting_key` ([String](../../sql-reference/data-types/string.md)) - The sorting key expression specified in the table.
@ -56,6 +58,7 @@ Columns:
- `comment` ([String](../../sql-reference/data-types/string.md)) - The comment for the table.
- `has_own_data` ([UInt8](../../sql-reference/data-types/int-uint.md)) - Flag that indicates whether the table itself stores some data on disk or only accesses some other source.
The `system.tables` table is used in `SHOW TABLES` query implementation.
@ -80,6 +83,7 @@ dependencies_database: []
dependencies_table: []
create_table_query: CREATE TABLE base.t1 (`n` UInt64) ENGINE = MergeTree ORDER BY n SETTINGS index_granularity = 8192
engine_full: MergeTree ORDER BY n SETTINGS index_granularity = 8192
as_select: SELECT database AS table_catalog
partition_key:
sorting_key: n
primary_key: n
@ -90,6 +94,7 @@ total_bytes: 99
lifetime_rows: ᴺᵁᴸᴸ
lifetime_bytes: ᴺᵁᴸᴸ
comment:
has_own_data: 0
Row 2:
──────
@ -105,6 +110,7 @@ dependencies_database: []
dependencies_table: []
create_table_query: CREATE TABLE default.`53r93yleapyears` (`id` Int8, `febdays` Int8) ENGINE = MergeTree ORDER BY id SETTINGS index_granularity = 8192
engine_full: MergeTree ORDER BY id SETTINGS index_granularity = 8192
as_select: SELECT name AS catalog_name
partition_key:
sorting_key: id
primary_key: id
@ -115,6 +121,5 @@ total_bytes: 155
lifetime_rows: ᴺᵁᴸᴸ
lifetime_bytes: ᴺᵁᴸᴸ
comment:
has_own_data: 0
```
[Original article](https://clickhouse.tech/docs/en/operations/system-tables/tables) <!--hide-->

2
docs/ru/sql-reference/functions/rounding-functions.md
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@ -173,7 +173,7 @@ roundBankers(4.5) = 4
roundBankers(3.55, 1) = 3.6
roundBankers(3.65, 1) = 3.6
roundBankers(10.35, 1) = 10.4
roundBankers(10.755, 2) = 11,76
roundBankers(10.755, 2) = 10,76
```
**Смотрите также**