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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).