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

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# 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.
The `system.columns` table contains the following columns (the column type is shown in brackets):
- `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.
2020-12-03 19:15:29 +00:00
**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:
2 rows in set. Elapsed: 0.002 sec.
```
[Original article](https://clickhouse.tech/docs/en/operations/system_tables/columns) <!--hide-->