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

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2020-06-22 08:45:22 +00:00
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# 系统。列 {#system-columns}
包含有关所有表中列的信息。
您可以使用此表获取类似于以下内容的信息 [DESCRIBE TABLE](../../sql-reference/statements/misc.md#misc-describe-table) 查询,但对于多个表一次。
`system.columns` 表包含以下列(列类型显示在括号中):
- `database` (String) — Database name.
- `table` (String) — Table name.
- `name` (String) — Column name.
- `type` (String) — Column type.
- `default_kind` (String) — Expression type (`DEFAULT`, `MATERIALIZED`, `ALIAS`)为默认值,如果没有定义,则为空字符串。
- `default_expression` (String) — Expression for the default value, or an empty string if it is not defined.
- `data_compressed_bytes` (UInt64) — The size of compressed data, in bytes.
- `data_uncompressed_bytes` (UInt64) — The size of decompressed data, in bytes.
- `marks_bytes` (UInt64) — The size of marks, in bytes.
- `comment` (String) — Comment on the column, or an empty string if it is not defined.
- `is_in_partition_key` (UInt8) — Flag that indicates whether the column is in the partition expression.
- `is_in_sorting_key` (UInt8) — Flag that indicates whether the column is in the sorting key expression.
- `is_in_primary_key` (UInt8) — Flag that indicates whether the column is in the primary key expression.
- `is_in_sampling_key` (UInt8) — Flag that indicates whether the column is in the sampling key expression.
2021-06-24 12:47:02 +00:00
[原文](https://clickhouse.tech/docs/zh/operations/system-tables/columns) <!--hide-->