Skip to main content

DESCRIBE TABLE

Returns information about table columns.

Syntax

DESC|DESCRIBE TABLE [db.]table [INTO OUTFILE filename] [FORMAT format]

The DESCRIBE statement returns a row for each table column with the following String values:

  • name — A column name.
  • type — A column type.
  • default_type — A clause that is used in the column default expression: DEFAULT, MATERIALIZED or ALIAS. If there is no default expression, then empty string is returned.
  • default_expression — An expression specified after the DEFAULT clause.
  • comment — A column comment.
  • codec_expression — A codec that is applied to the column.
  • ttl_expression — A TTL expression.
  • 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 setting.

All columns in Nested data structures are described separately. The name of each column is prefixed with a parent column name and a dot.

To show internal subcolumns of other data types, use the describe_include_subcolumns setting.

Example

Query:

CREATE TABLE describe_example (
id UInt64, text String DEFAULT 'unknown' CODEC(ZSTD),
user Tuple (name String, age UInt8)
) ENGINE = MergeTree() ORDER BY id;

DESCRIBE TABLE describe_example;
DESCRIBE TABLE describe_example SETTINGS describe_include_subcolumns=1;

Result:

┌─name─┬─type──────────────────────────┬─default_type─┬─default_expression─┬─comment─┬─codec_expression─┬─ttl_expression─┐
│ id │ UInt64 │ │ │ │ │ │
│ text │ String │ DEFAULT │ 'unknown' │ │ ZSTD(1) │ │
│ user │ Tuple(name String, age UInt8) │ │ │ │ │ │
└──────┴───────────────────────────────┴──────────────┴────────────────────┴─────────┴──────────────────┴────────────────┘

The second query additionally shows subcolumns:

┌─name──────┬─type──────────────────────────┬─default_type─┬─default_expression─┬─comment─┬─codec_expression─┬─ttl_expression─┬─is_subcolumn─┐
│ id │ UInt64 │ │ │ │ │ │ 0 │
│ text │ String │ DEFAULT │ 'unknown' │ │ ZSTD(1) │ │ 0 │
│ user │ Tuple(name String, age UInt8) │ │ │ │ │ │ 0 │
│ user.name │ String │ │ │ │ │ │ 1 │
│ user.age │ UInt8 │ │ │ │ │ │ 1 │
└───────────┴───────────────────────────────┴──────────────┴────────────────────┴─────────┴──────────────────┴────────────────┴──────────────┘

See Also