mirror of https://github.com/ClickHouse/ClickHouse.git synced 2024-12-14 02:12:21 +00:00

2024-08-08 11:21:23 +00:00

slug	sidebar_position	sidebar_label
/en/sql-reference/statements/alter/statistics	45	STATISTICS

Manipulating Column Statistics

The following operations are available:

ALTER TABLE [db].table ADD STATISTICS [IF NOT EXISTS] (column list) TYPE (type list) - Adds statistic description to tables metadata.
ALTER TABLE [db].table MODIFY STATISTICS (column list) TYPE (type list) - Modifies statistic description to tables metadata.
ALTER TABLE [db].table DROP STATISTICS [IF EXISTS] (column list) - Removes statistics from the metadata of the specified columns and deletes all statistics objects in all parts for the specified columns.
ALTER TABLE [db].table CLEAR STATISTICS [IF EXISTS] (column list) - Deletes all statistics objects in all parts for the specified columns. Statistics objects can be rebuild using ALTER TABLE MATERIALIZE STATISTICS.
ALTER TABLE [db.]table MATERIALIZE STATISTICS [IF EXISTS] (column list) - Rebuilds the statistic for columns. Implemented as a mutation.

The first two commands are lightweight in a sense that they only change metadata or remove files.

Also, they are replicated, syncing statistics metadata via ZooKeeper.

Example:

Adding two statistics types to two columns:

ALTER TABLE t1 MODIFY STATISTICS c, d TYPE TDigest, Uniq;

:::note Statistic are supported only for *MergeTree engine tables (including replicated variants). :::