mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-18 05:32:52 +00:00
70 lines
4.7 KiB
Markdown
70 lines
4.7 KiB
Markdown
---
|
|
slug: /en/sql-reference/statements/describe-table
|
|
sidebar_position: 42
|
|
sidebar_label: DESCRIBE TABLE
|
|
title: "DESCRIBE TABLE"
|
|
---
|
|
|
|
Returns information about table columns.
|
|
|
|
**Syntax**
|
|
|
|
``` sql
|
|
DESC|DESCRIBE TABLE [db.]table [INTO OUTFILE filename] [FORMAT format]
|
|
```
|
|
|
|
The `DESCRIBE` statement returns a row for each table column with the following [String](../../sql-reference/data-types/string.md) values:
|
|
|
|
- `name` — A column name.
|
|
- `type` — A column type.
|
|
- `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.
|
|
- `default_expression` — An expression specified after the `DEFAULT` clause.
|
|
- `comment` — A [column comment](../../sql-reference/statements/alter/column.md#alter_comment-column).
|
|
- `codec_expression` — A [codec](../../sql-reference/statements/create/table.md#codecs) that is applied to the column.
|
|
- `ttl_expression` — A [TTL](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-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](../../operations/settings/settings.md#describe_include_subcolumns) setting.
|
|
|
|
All columns in [Nested](../../sql-reference/data-types/nested-data-structures/index.md) 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](../../operations/settings/settings.md#describe_include_subcolumns) setting.
|
|
|
|
**Example**
|
|
|
|
Query:
|
|
|
|
``` sql
|
|
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:
|
|
|
|
``` text
|
|
┌─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:
|
|
|
|
``` text
|
|
┌─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**
|
|
|
|
- [describe_include_subcolumns](../../operations/settings/settings.md#describe_include_subcolumns) setting.
|