mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-27 10:02:01 +00:00
403 lines
21 KiB
Markdown
403 lines
21 KiB
Markdown
---
|
|
slug: /en/operations/system-tables/information_schema
|
|
---
|
|
# INFORMATION_SCHEMA
|
|
|
|
`INFORMATION_SCHEMA` (or: `information_schema`) is a system database which provides a (somewhat) standardized, [DBMS-agnostic view](https://en.wikipedia.org/wiki/Information_schema) on metadata of database objects. The views in `INFORMATION_SCHEMA` are generally inferior to normal system tables but tools can use them to obtain basic information in a cross-DBMS manner. The structure and content of views in `INFORMATION_SCHEMA` is supposed to evolves in a backwards-compatible way, i.e. only new functionality is added but existing functionality is not changed or removed. In terms of internal implementation, views in `INFORMATION_SCHEMA` usually map to to normal system tables like [system.columns](../../operations/system-tables/columns.md), [system.databases](../../operations/system-tables/databases.md) and [system.tables](../../operations/system-tables/tables.md).
|
|
|
|
``` sql
|
|
SHOW TABLES FROM INFORMATION_SCHEMA;
|
|
|
|
-- or:
|
|
SHOW TABLES FROM information_schema;
|
|
```
|
|
|
|
``` text
|
|
┌─name────────────────────┐
|
|
│ COLUMNS │
|
|
│ KEY_COLUMN_USAGE │
|
|
│ REFERENTIAL_CONSTRAINTS │
|
|
│ SCHEMATA │
|
|
| STATISTICS |
|
|
│ TABLES │
|
|
│ VIEWS │
|
|
│ columns │
|
|
│ key_column_usage │
|
|
│ referential_constraints │
|
|
│ schemata │
|
|
| statistics |
|
|
│ tables │
|
|
│ views │
|
|
└─────────────────────────┘
|
|
```
|
|
|
|
`INFORMATION_SCHEMA` contains the following views:
|
|
|
|
- [COLUMNS](#columns)
|
|
- [KEY_COLUMN_USAGE](#key_column_usage)
|
|
- [REFERENTIAL_CONSTRAINTS](#referential_constraints)
|
|
- [SCHEMATA](#schemata)
|
|
- [STATISTICS](#statistics)
|
|
- [TABLES](#tables)
|
|
- [VIEWS](#views)
|
|
|
|
Case-insensitive equivalent views, e.g. `INFORMATION_SCHEMA.columns` are provided for reasons of compatibility with other databases. The same applies to all the columns in these views - both lowercase (for example, `table_name`) and uppercase (`TABLE_NAME`) variants are provided.
|
|
|
|
## 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 bit width 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.
|
|
- `extra` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — `STORED GENERATED` for `MATERIALIZED`-type columns, `VIRTUAL GENERATED` for `ALIAS`-type columns, `DEFAULT_GENERATED` for `DEFAULT`-type columns, or `NULL`.
|
|
|
|
**Example**
|
|
|
|
Query:
|
|
|
|
``` sql
|
|
SELECT table_catalog,
|
|
table_schema,
|
|
table_name,
|
|
column_name,
|
|
ordinal_position,
|
|
column_default,
|
|
is_nullable,
|
|
data_type,
|
|
character_maximum_length,
|
|
character_octet_length,
|
|
numeric_precision,
|
|
numeric_precision_radix,
|
|
numeric_scale,
|
|
datetime_precision,
|
|
character_set_catalog,
|
|
character_set_schema,
|
|
character_set_name,
|
|
collation_catalog,
|
|
collation_schema,
|
|
collation_name,
|
|
domain_catalog,
|
|
domain_schema,
|
|
domain_name,
|
|
column_comment,
|
|
column_type
|
|
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 catalog_name,
|
|
schema_name,
|
|
schema_owner,
|
|
default_character_set_catalog,
|
|
default_character_set_schema,
|
|
default_character_set_name,
|
|
sql_path
|
|
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` ([String](../../sql-reference/data-types/string.md)) — Table type. Possible values:
|
|
- `BASE TABLE`
|
|
- `VIEW`
|
|
- `FOREIGN TABLE`
|
|
- `LOCAL TEMPORARY`
|
|
- `SYSTEM VIEW`
|
|
- `table_rows` ([Nullable](../../sql-reference/data-types/nullable.md)([UInt64](../../sql-reference/data-types/int-uint.md))) — The total
|
|
number of rows. NULL if it could not be determined.
|
|
- `data_length` ([Nullable](../../sql-reference/data-types/nullable.md)([UInt64](../../sql-reference/data-types/int-uint.md))) — The size of
|
|
the data on-disk. NULL if it could not be determined.
|
|
- `table_collation` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — The table default collation. Always `utf8mb4_0900_ai_ci`.
|
|
- `table_comment` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — The comment used when creating the table.
|
|
|
|
**Example**
|
|
|
|
Query:
|
|
|
|
``` sql
|
|
SELECT table_catalog,
|
|
table_schema,
|
|
table_name,
|
|
table_type,
|
|
table_collation,
|
|
table_comment
|
|
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
|
|
table_collation: utf8mb4_0900_ai_ci
|
|
table_comment:
|
|
```
|
|
|
|
## 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 table_catalog,
|
|
table_schema,
|
|
table_name,
|
|
view_definition,
|
|
check_option,
|
|
is_updatable,
|
|
is_insertable_into,
|
|
is_trigger_updatable,
|
|
is_trigger_deletable,
|
|
is_trigger_insertable_into
|
|
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
|
|
```
|
|
|
|
## KEY_COLUMN_USAGE {#key_column_usage}
|
|
|
|
Contains columns from the [system.tables](../../operations/system-tables/tables.md) system table which are restricted by constraints.
|
|
|
|
Columns:
|
|
|
|
- `constraint_catalog` ([String](../../sql-reference/data-types/string.md)) — Currently unused. Always `def`.
|
|
- `constraint_schema` ([String](../../sql-reference/data-types/string.md)) — The name of the schema (database) to which the constraint belongs.
|
|
- `constraint_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — The name of the constraint.
|
|
- `table_catalog` ([String](../../sql-reference/data-types/string.md)) — Currently unused. Always `def`.
|
|
- `table_schema` ([String](../../sql-reference/data-types/string.md)) — The name of the schema (database) to which the table belongs.
|
|
- `table_name` ([String](../../sql-reference/data-types/string.md)) — The name of the table that has the constraint.
|
|
- `column_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — The name of the column that has the constraint.
|
|
- `ordinal_position` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Currently unused. Always `1`.
|
|
- `position_in_unique_constraint` ([Nullable](../../sql-reference/data-types/nullable.md)([UInt32](../../sql-reference/data-types/int-uint.md))) — Currently unused. Always `NULL`.
|
|
- `referenced_table_schema` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — Currently unused. Always NULL.
|
|
- `referenced_table_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — Currently unused. Always NULL.
|
|
- `referenced_column_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — Currently unused. Always NULL.
|
|
|
|
**Example**
|
|
|
|
```sql
|
|
CREATE TABLE test (i UInt32, s String) ENGINE MergeTree ORDER BY i;
|
|
SELECT constraint_catalog,
|
|
constraint_schema,
|
|
constraint_name,
|
|
table_catalog,
|
|
table_schema,
|
|
table_name,
|
|
column_name,
|
|
ordinal_position,
|
|
position_in_unique_constraint,
|
|
referenced_table_schema,
|
|
referenced_table_name,
|
|
referenced_column_name
|
|
FROM information_schema.key_column_usage
|
|
WHERE table_name = 'test'
|
|
FORMAT Vertical;
|
|
```
|
|
|
|
Result:
|
|
|
|
```
|
|
Row 1:
|
|
──────
|
|
constraint_catalog: def
|
|
constraint_schema: default
|
|
constraint_name: PRIMARY
|
|
table_catalog: def
|
|
table_schema: default
|
|
table_name: test
|
|
column_name: i
|
|
ordinal_position: 1
|
|
position_in_unique_constraint: ᴺᵁᴸᴸ
|
|
referenced_table_schema: ᴺᵁᴸᴸ
|
|
referenced_table_name: ᴺᵁᴸᴸ
|
|
referenced_column_name: ᴺᵁᴸᴸ
|
|
```
|
|
|
|
## REFERENTIAL_CONSTRAINTS {#referential_constraints}
|
|
|
|
Contains information about foreign keys. Currently returns an empty result (no rows) which is just enough to provide compatibility with 3rd party tools like Tableau Online.
|
|
|
|
Columns:
|
|
|
|
- `constraint_catalog` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `constraint_schema` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `constraint_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — Currently unused.
|
|
- `unique_constraint_catalog` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `unique_constraint_schema` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `unique_constraint_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — Currently unused.
|
|
- `match_option` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `update_rule` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `delete_rule` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `table_name` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `referenced_table_name` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
|
|
## STATISTICS {#statistics}
|
|
|
|
Provides information about table indexes. Currently returns an empty result (no rows) which is just enough to provide compatibility with 3rd party tools like Tableau Online.
|
|
|
|
Columns:
|
|
|
|
- `table_catalog` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `table_schema` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `table_name` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `non_unique` ([Int32](../../sql-reference/data-types/int-uint.md)) — Currently unused.
|
|
- `index_schema` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `index_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — Currently unused.
|
|
- `seq_in_index` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Currently unused.
|
|
- `column_name` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — Currently unused.
|
|
- `collation` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — Currently unused.
|
|
- `cardinality` ([Nullable](../../sql-reference/data-types/nullable.md)([Int64](../../sql-reference/data-types/int-uint.md))) — Currently unused.
|
|
- `sub_part` ([Nullable](../../sql-reference/data-types/nullable.md)([Int64](../../sql-reference/data-types/int-uint.md))) — Currently unused.
|
|
- `packed` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — Currently unused.
|
|
- `nullable` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `index_type` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `comment` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `index_comment` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `is_visible` ([String](../../sql-reference/data-types/string.md)) — Currently unused.
|
|
- `expression` ([Nullable](../../sql-reference/data-types/nullable.md)([String](../../sql-reference/data-types/string.md))) — Currently unused.
|