Create information_schema

Задокументировал information_schema.

docs/en/operations/system-tables/columns.md

@@ -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
+database:                INFORMATION_SCHEMA
-table:                   aggregate_function_combinators
+table:                   COLUMNS
-name:                    name
+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
+database:                INFORMATION_SCHEMA
-table:                   aggregate_function_combinators
+table:                   COLUMNS
-name:                    is_internal
+name:                    table_schema
-type:                    UInt8
+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):

docs/en/operations/system-tables/databases.md

@@ -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─┐
+┌─name───────────────┬─engine─┬─data_path──────────────────┬─metadata_path───────────────────────────────────────────────────────┬─uuid─────────────────────────────────┬─comment─┐
-│ _temporary_and_external_tables │ Memory │ /var/lib/clickhouse/       │                                                                     │ 00000000-0000-0000-0000-000000000000 │
+│ 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/ │ d317b4bd-3595-4386-81ee-c2334694128a │
+│ default            │ Atomic │ /var/lib/clickhouse/store/ │ /var/lib/clickhouse/store/d31/d317b4bd-3595-4386-81ee-c2334694128a/ │ 24363899-31d7-42a0-a436-389931d752a0 │         │
-│ test                           │ Atomic │ /var/lib/clickhouse/store/ │ /var/lib/clickhouse/store/39b/39bf0cc5-4c06-4717-87fe-c75ff3bd8ebb/ │ 39bf0cc5-4c06-4717-87fe-c75ff3bd8ebb │
+│ 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/ │ 1d1c869d-e465-4b1b-a51f-be033436ebf9 │
+│ 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-->

docs/en/operations/system-tables/information_schema.md

@@ -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).

docs/en/operations/system-tables/tables.md

@@ -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-->

docs/ru/sql-reference/functions/rounding-functions.md

@@ -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**