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

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系统。列

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 查询，但对于多个表一次。

该 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.

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