mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-24 08:32:02 +00:00
214 lines
12 KiB
Markdown
214 lines
12 KiB
Markdown
---
|
|
slug: /en/operations/system-tables/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. These views read data from the columns of the [system.columns](../../operations/system-tables/columns.md), [system.databases](../../operations/system-tables/databases.md) and [system.tables](../../operations/system-tables/tables.md) system tables.
|
|
|
|
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:
|
|
|
|
- [COLUMNS](#columns)
|
|
- [SCHEMATA](#schemata)
|
|
- [TABLES](#tables)
|
|
- [VIEWS](#views)
|
|
|
|
## COLUMNS {#columns}
|
|
|
|
Contains columns read from the [system.columns](../../operations/system-tables/columns.md) system table and columns that are not supported in ClickHouse or do not make sense (always `NULL`), but must be by the standard.
|
|
|
|
Columns:
|
|
|
|
- `table_catalog` ([String](../../sql-reference/data-types/string.md)) — The name of the database in which the table is located.
|
|
- `table_schema` ([String](../../sql-reference/data-types/string.md)) — The name of the database in which the table is located.
|
|
- `table_name` ([String](../../sql-reference/data-types/string.md)) — Table name.
|
|
- `column_name` ([String](../../sql-reference/data-types/string.md)) — Column name.
|
|
- `ordinal_position` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Ordinal position of a column in a table starting with 1.
|
|
- `column_default` ([String](../../sql-reference/data-types/string.md)) — Expression for the default value, or an empty string if it is not defined.
|
|
- `is_nullable` ([UInt8](../../sql-reference/data-types/int-uint.md)) — Flag that indicates whether the column type is `Nullable`.
|
|
- `data_type` ([String](../../sql-reference/data-types/string.md)) — Column type.
|
|
- `character_maximum_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. In ClickHouse makes sense only for `FixedString` data type. Otherwise, the `NULL` value is returned.
|
|
- `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. In ClickHouse makes sense only for `FixedString` data type. Otherwise, the `NULL` value is returned.
|
|
- `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. In ClickHouse it is bitness for integer types and decimal precision for `Decimal` types. 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. In ClickHouse it's 2 for integer types and 10 for `Decimal` types. 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. In ClickHouse makes sense only for `Decimal` types. Otherwise, the `NULL` value is returned.
|
|
- `datetime_precision` ([Nullable](../../sql-reference/data-types/nullable.md)([UInt64](../../sql-reference/data-types/int-uint.md))) — Decimal precision of `DateTime64` data type. For other data types, the `NULL` value is returned.
|
|
- `character_set_catalog` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `character_set_schema` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `character_set_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `collation_catalog` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `collation_schema` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `collation_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `domain_catalog` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `domain_schema` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `domain_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
|
|
**Example**
|
|
|
|
Query:
|
|
|
|
``` sql
|
|
SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE (table_schema=currentDatabase() OR table_schema='') AND table_name NOT LIKE '%inner%' LIMIT 1 FORMAT Vertical;
|
|
```
|
|
|
|
Result:
|
|
|
|
``` 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
|
|
```
|
|
|
|
## SCHEMATA {#schemata}
|
|
|
|
Contains columns read from the [system.databases](../../operations/system-tables/databases.md) system table and columns that are not supported in ClickHouse or do not make sense (always `NULL`), but must be by the standard.
|
|
|
|
Columns:
|
|
|
|
- `catalog_name` ([String](../../sql-reference/data-types/string.md)) — The name of the database.
|
|
- `schema_name` ([String](../../sql-reference/data-types/string.md)) — The name of the database.
|
|
- `schema_owner` ([String](../../sql-reference/data-types/string.md)) — Schema owner name, always `'default'`.
|
|
- `default_character_set_catalog` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `default_character_set_schema` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `default_character_set_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
- `sql_path` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `NULL`, not supported.
|
|
|
|
**Example**
|
|
|
|
Query:
|
|
|
|
``` sql
|
|
SELECT * FROM information_schema.schemata WHERE schema_name ILIKE 'information_schema' LIMIT 1 FORMAT Vertical;
|
|
```
|
|
|
|
Result:
|
|
|
|
``` 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 {#tables}
|
|
|
|
Contains columns read from the [system.tables](../../operations/system-tables/tables.md) system table.
|
|
|
|
Columns:
|
|
|
|
- `table_catalog` ([String](../../sql-reference/data-types/string.md)) — The name of the database in which the table is located.
|
|
- `table_schema` ([String](../../sql-reference/data-types/string.md)) — The name of the database in which the table is located.
|
|
- `table_name` ([String](../../sql-reference/data-types/string.md)) — Table name.
|
|
- `table_type` ([Enum8](../../sql-reference/data-types/enum.md)) — Table type. Possible values:
|
|
- `BASE TABLE`
|
|
- `VIEW`
|
|
- `FOREIGN TABLE`
|
|
- `LOCAL TEMPORARY`
|
|
- `SYSTEM VIEW`
|
|
|
|
**Example**
|
|
|
|
Query:
|
|
|
|
``` sql
|
|
SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE (table_schema = currentDatabase() OR table_schema = '') AND table_name NOT LIKE '%inner%' LIMIT 1 FORMAT Vertical;
|
|
```
|
|
|
|
Result:
|
|
|
|
``` text
|
|
Row 1:
|
|
──────
|
|
table_catalog: default
|
|
table_schema: default
|
|
table_name: describe_example
|
|
table_type: BASE TABLE
|
|
```
|
|
|
|
## VIEWS {#views}
|
|
|
|
Contains columns read from the [system.tables](../../operations/system-tables/tables.md) system table, when the table engine [View](../../engines/table-engines/special/view.md) is used.
|
|
|
|
Columns:
|
|
|
|
- `table_catalog` ([String](../../sql-reference/data-types/string.md)) — The name of the database in which the table is located.
|
|
- `table_schema` ([String](../../sql-reference/data-types/string.md)) — The name of the database in which the table is located.
|
|
- `table_name` ([String](../../sql-reference/data-types/string.md)) — Table name.
|
|
- `view_definition` ([String](../../sql-reference/data-types/string.md)) — `SELECT` query for view.
|
|
- `check_option` ([String](../../sql-reference/data-types/string.md)) — `NONE`, no checking.
|
|
- `is_updatable` ([Enum8](../../sql-reference/data-types/enum.md)) — `NO`, the view is not updated.
|
|
- `is_insertable_into` ([Enum8](../../sql-reference/data-types/enum.md)) — Shows whether the created view is [materialized](../../sql-reference/statements/create/view.md/#materialized-view). Possible values:
|
|
- `NO` — The created view is not materialized.
|
|
- `YES` — The created view is materialized.
|
|
- `is_trigger_updatable` ([Enum8](../../sql-reference/data-types/enum.md)) — `NO`, the trigger is not updated.
|
|
- `is_trigger_deletable` ([Enum8](../../sql-reference/data-types/enum.md)) — `NO`, the trigger is not deleted.
|
|
- `is_trigger_insertable_into` ([Enum8](../../sql-reference/data-types/enum.md)) — `NO`, no data is inserted into the trigger.
|
|
|
|
**Example**
|
|
|
|
Query:
|
|
|
|
``` 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() LIMIT 1 FORMAT Vertical;
|
|
```
|
|
|
|
Result:
|
|
|
|
``` 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
|
|
```
|