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
β A column name.type
β A column type.default_type
β A clause that is used in the column default expression:DEFAULT
,MATERIALIZED
orALIAS
. If there is no default expression, then empty string is returned.default_expression
β An expression specified after theDEFAULT
clause.comment
β A column comment.codec_expression
β A codec that is applied to the column.ttl_expression
β A TTL expression.is_subcolumn
β A flag that equals1
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:
ββnameββ¬βtypeβββββββββββββββββββββββββββ¬βdefault_typeββ¬βdefault_expressionββ¬βcommentββ¬βcodec_expressionββ¬βttl_expressionββ
β id β UInt64 β β β β β β
β text β String β DEFAULT β 'unknown' β β ZSTD(1) β β
β user β Tuple(name String, age UInt8) β β β β β β
ββββββββ΄ββββββββββββββββββββββββββββββββ΄βββββββββββββββ΄βββββββββββββββββββββ΄ββββββββββ΄βββββββββββββββββββ΄βββββββββββββββββ
The second query additionally shows subcolumns:
ββnameβββββββ¬βtypeβββββββββββββββββββββββββββ¬βdefault_typeββ¬βdefault_expressionββ¬βcommentββ¬βcodec_expressionββ¬βttl_expressionββ¬βis_subcolumnββ
β id β UInt64 β β β β β β 0 β
β text β String β DEFAULT β 'unknown' β β ZSTD(1) β β 0 β
β user β Tuple(name String, age UInt8) β β β β β β 0 β
β user.name β String β β β β β β 1 β
β user.age β UInt8 β β β β β β 1 β
βββββββββββββ΄ββββββββββββββββββββββββββββββββ΄βββββββββββββββ΄βββββββββββββββββββββ΄ββββββββββ΄βββββββββββββββββββ΄βββββββββββββββββ΄βββββββββββββββ
See Also
- describe_include_subcolumns setting.