mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-18 20:32:43 +00:00
20 lines
717 B
Markdown
20 lines
717 B
Markdown
---
|
|
sidebar_position: 41
|
|
sidebar_label: SAMPLE BY
|
|
---
|
|
|
|
# Manipulating Sampling-Key Expressions
|
|
|
|
Syntax:
|
|
|
|
``` sql
|
|
ALTER TABLE [db].name [ON CLUSTER cluster] MODIFY SAMPLE BY new_expression
|
|
```
|
|
|
|
The command changes the [sampling key](../../../engines/table-engines/mergetree-family/mergetree.md) of the table to `new_expression` (an expression or a tuple of expressions).
|
|
|
|
The command is lightweight in the sense that it only changes metadata. The primary key must contain the new sample key.
|
|
|
|
:::note
|
|
It only works for tables in the [MergeTree](../../../engines/table-engines/mergetree-family/mergetree.md) family (including [replicated](../../../engines/table-engines/mergetree-family/replication.md) tables).
|
|
::: |