ALTER TABLE ... DELETE Statement

Documentation for ALTER TABLE … DELETE Statement

ALTER TABLE [db.]table [ON CLUSTER cluster] DELETE WHERE filter_expr

Deletes data matching the specified filtering expression. Implemented as a mutation.

The ALTER TABLE prefix makes this syntax different from most other systems supporting SQL. It is intended to signify that unlike similar queries in OLTP databases this is a heavy operation not designed for frequent use. ALTER TABLE is considered a heavyweight operation that requires the underlying data to be merged before it is deleted. For MergeTree tables, consider using the DELETE FROM query, which performs a lightweight delete and can be considerably faster.

The filter_expr must be of type UInt8. The query deletes rows in the table for which this expression takes a non-zero value.

One query can contain several commands separated by commas.

The synchronicity of the query processing is defined by the mutations_sync setting. By default, it is asynchronous.

See also

• Mutations
• Synchronicity of ALTER Queries
• mutations_sync setting

Related content

• Blog: Handling Updates and Deletes in ClickHouse