ClickHouse/docs/en/sql-reference/statements/alter/sample-by.md

slug	sidebar_position	sidebar_label	title
/en/sql-reference/statements/alter/sample-by	41	SAMPLE BY	Manipulating Sampling-Key Expressions

Manipulating SAMPLE BY expression

The following operations are available:

MODIFY

ALTER TABLE [db].name [ON CLUSTER cluster] MODIFY SAMPLE BY new_expression

The command changes the sampling key of the table to new_expression (an expression or a tuple of expressions). The primary key must contain the new sample key.

REMOVE

ALTER TABLE [db].name [ON CLUSTER cluster] REMOVE SAMPLE BY

The command removes the sampling key of the table.

The commands MODIFY and REMOVE are lightweight in the sense that they only change metadata or remove files.

:::note
It only works for tables in the MergeTree family (including replicated tables). :::