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23 lines
1.5 KiB
Markdown
23 lines
1.5 KiB
Markdown
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# system.columns {#system-columns}
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Contains information about columns in all the tables.
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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.
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The `system.columns` table contains the following columns (the column type is shown in brackets):
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- `database` (String) — Database name.
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- `table` (String) — Table name.
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- `name` (String) — Column name.
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- `type` (String) — Column type.
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- `default_kind` (String) — Expression type (`DEFAULT`, `MATERIALIZED`, `ALIAS`) for the default value, or an empty string if it is not defined.
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- `default_expression` (String) — Expression for the default value, or an empty string if it is not defined.
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- `data_compressed_bytes` (UInt64) — The size of compressed data, in bytes.
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- `data_uncompressed_bytes` (UInt64) — The size of decompressed data, in bytes.
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- `marks_bytes` (UInt64) — The size of marks, in bytes.
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- `comment` (String) — Comment on the column, or an empty string if it is not defined.
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- `is_in_partition_key` (UInt8) — Flag that indicates whether the column is in the partition expression.
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- `is_in_sorting_key` (UInt8) — Flag that indicates whether the column is in the sorting key expression.
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- `is_in_primary_key` (UInt8) — Flag that indicates whether the column is in the primary key expression.
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- `is_in_sampling_key` (UInt8) — Flag that indicates whether the column is in the sampling key expression.
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