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

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41	ORDER BY

Manipulating Key Expressions

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

The command changes the sorting key of the table to new_expression (an expression or a tuple of expressions). Primary key remains the same.

The command is lightweight in a sense that it only changes metadata. To keep the property that data part rows are ordered by the sorting key expression you cannot add expressions containing existing columns to the sorting key (only columns added by the ADD COLUMN command in the same ALTER query, without default column value).

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