mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-27 10:02:01 +00:00
73 lines
3.6 KiB
Markdown
73 lines
3.6 KiB
Markdown
# system.columns {#system-columns}
|
|
|
|
Contains information about columns in all the tables.
|
|
|
|
You can use this table to get information similar to the [DESCRIBE TABLE](../../sql-reference/statements/misc.md#misc-describe-table) query, but for multiple tables at once.
|
|
|
|
Columns from [temporary tables](../../sql-reference/statements/create/table.md#temporary-tables) are visible in the `system.columns` only in those session where they have been created. They are shown with the empty `database` field.
|
|
|
|
Columns:
|
|
|
|
- `database` ([String](../../sql-reference/data-types/string.md)) — Database name.
|
|
- `table` ([String](../../sql-reference/data-types/string.md)) — Table name.
|
|
- `name` ([String](../../sql-reference/data-types/string.md)) — Column name.
|
|
- `type` ([String](../../sql-reference/data-types/string.md)) — Column type.
|
|
- `position` ([UInt64](../../sql-reference/data-types/int-uint.md)) — Ordinal position of a column in a table starting with 1.
|
|
- `default_kind` ([String](../../sql-reference/data-types/string.md)) — Expression type (`DEFAULT`, `MATERIALIZED`, `ALIAS`) for the default value, or an empty string if it is not defined.
|
|
- `default_expression` ([String](../../sql-reference/data-types/string.md)) — Expression for the default value, or an empty string if it is not defined.
|
|
- `data_compressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The size of compressed data, in bytes.
|
|
- `data_uncompressed_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The size of decompressed data, in bytes.
|
|
- `marks_bytes` ([UInt64](../../sql-reference/data-types/int-uint.md)) — The size of marks, in bytes.
|
|
- `comment` ([String](../../sql-reference/data-types/string.md)) — Comment on the column, or an empty string if it is not defined.
|
|
- `is_in_partition_key` ([UInt8](../../sql-reference/data-types/int-uint.md)) — Flag that indicates whether the column is in the partition expression.
|
|
- `is_in_sorting_key` ([UInt8](../../sql-reference/data-types/int-uint.md)) — Flag that indicates whether the column is in the sorting key expression.
|
|
- `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.
|
|
|
|
**Example**
|
|
|
|
```sql
|
|
SELECT * FROM system.columns LIMIT 2 FORMAT Vertical;
|
|
```
|
|
|
|
```text
|
|
Row 1:
|
|
──────
|
|
database: system
|
|
table: aggregate_function_combinators
|
|
name: name
|
|
type: String
|
|
default_kind:
|
|
default_expression:
|
|
data_compressed_bytes: 0
|
|
data_uncompressed_bytes: 0
|
|
marks_bytes: 0
|
|
comment:
|
|
is_in_partition_key: 0
|
|
is_in_sorting_key: 0
|
|
is_in_primary_key: 0
|
|
is_in_sampling_key: 0
|
|
compression_codec:
|
|
|
|
Row 2:
|
|
──────
|
|
database: system
|
|
table: aggregate_function_combinators
|
|
name: is_internal
|
|
type: UInt8
|
|
default_kind:
|
|
default_expression:
|
|
data_compressed_bytes: 0
|
|
data_uncompressed_bytes: 0
|
|
marks_bytes: 0
|
|
comment:
|
|
is_in_partition_key: 0
|
|
is_in_sorting_key: 0
|
|
is_in_primary_key: 0
|
|
is_in_sampling_key: 0
|
|
compression_codec:
|
|
```
|
|
|
|
[Original article](https://clickhouse.tech/docs/en/operations/system_tables/columns) <!--hide-->
|