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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).