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70 lines
4.6 KiB
Markdown
70 lines
4.6 KiB
Markdown
---
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sidebar_position: 42
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sidebar_label: DESCRIBE
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---
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# DESCRIBE TABLE
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Returns information about table columns.
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**Syntax**
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``` sql
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DESC|DESCRIBE TABLE [db.]table [INTO OUTFILE filename] [FORMAT format]
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```
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The `DESCRIBE` statement returns a row for each table column with the following [String](../../sql-reference/data-types/string.md) values:
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- `name` — A column name.
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- `type` — A column type.
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- `default_type` — A clause that is used in the column [default expression](../../sql-reference/statements/create/table.md#create-default-values): `DEFAULT`, `MATERIALIZED` or `ALIAS`. If there is no default expression, then empty string is returned.
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- `default_expression` — An expression specified after the `DEFAULT` clause.
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- `comment` — A [column comment](../../sql-reference/statements/alter/column.md#alter_comment-column).
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- `codec_expression` — A [codec](../../sql-reference/statements/create/table.md#codecs) that is applied to the column.
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- `ttl_expression` — A [TTL](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-ttl) expression.
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- `is_subcolumn` — A flag that equals `1` for internal subcolumns. It is included into the result only if subcolumn description is enabled by the [describe_include_subcolumns](../../operations/settings/settings.md#describe_include_subcolumns) setting.
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All columns in [Nested](../../sql-reference/data-types/nested-data-structures/nested.md) data structures are described separately. The name of each column is prefixed with a parent column name and a dot.
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To show internal subcolumns of other data types, use the [describe_include_subcolumns](../../operations/settings/settings.md#describe_include_subcolumns) setting.
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**Example**
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Query:
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``` sql
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CREATE TABLE describe_example (
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id UInt64, text String DEFAULT 'unknown' CODEC(ZSTD),
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user Tuple (name String, age UInt8)
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) ENGINE = MergeTree() ORDER BY id;
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DESCRIBE TABLE describe_example;
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DESCRIBE TABLE describe_example SETTINGS describe_include_subcolumns=1;
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```
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Result:
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``` text
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┌─name─┬─type──────────────────────────┬─default_type─┬─default_expression─┬─comment─┬─codec_expression─┬─ttl_expression─┐
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│ id │ UInt64 │ │ │ │ │ │
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│ text │ String │ DEFAULT │ 'unknown' │ │ ZSTD(1) │ │
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│ user │ Tuple(name String, age UInt8) │ │ │ │ │ │
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└──────┴───────────────────────────────┴──────────────┴────────────────────┴─────────┴──────────────────┴────────────────┘
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```
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The second query additionally shows subcolumns:
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``` text
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┌─name──────┬─type──────────────────────────┬─default_type─┬─default_expression─┬─comment─┬─codec_expression─┬─ttl_expression─┬─is_subcolumn─┐
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│ id │ UInt64 │ │ │ │ │ │ 0 │
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│ text │ String │ DEFAULT │ 'unknown' │ │ ZSTD(1) │ │ 0 │
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│ user │ Tuple(name String, age UInt8) │ │ │ │ │ │ 0 │
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│ user.name │ String │ │ │ │ │ │ 1 │
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│ user.age │ UInt8 │ │ │ │ │ │ 1 │
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└───────────┴───────────────────────────────┴──────────────┴────────────────────┴─────────┴──────────────────┴────────────────┴──────────────┘
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```
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**See Also**
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- [describe_include_subcolumns](../../operations/settings/settings.md#describe_include_subcolumns) setting.
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