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36 lines
1.6 KiB
Markdown
36 lines
1.6 KiB
Markdown
---
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slug: /en/sql-reference/statements/alter/statistics
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sidebar_position: 45
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sidebar_label: STATISTICS
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---
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# Manipulating Column Statistics
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The following operations are available:
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- `ALTER TABLE [db].table ADD STATISTICS [IF NOT EXISTS] (column list) TYPE (type list)` - Adds statistic description to tables metadata.
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- `ALTER TABLE [db].table MODIFY STATISTICS (column list) TYPE (type list)` - Modifies statistic description to tables metadata.
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- `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.
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- `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`.
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- `ALTER TABLE [db.]table MATERIALIZE STATISTICS [IF EXISTS] (column list)` - Rebuilds the statistic for columns. Implemented as a [mutation](../../../sql-reference/statements/alter/index.md#mutations).
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The first two commands are lightweight in a sense that they only change metadata or remove files.
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Also, they are replicated, syncing statistics metadata via ZooKeeper.
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## Example:
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Adding two statistics types to two columns:
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```
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ALTER TABLE t1 MODIFY STATISTICS c, d TYPE TDigest, Uniq;
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```
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:::note
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Statistic are supported only for [`*MergeTree`](../../../engines/table-engines/mergetree-family/mergetree.md) engine tables (including [replicated](../../../engines/table-engines/mergetree-family/replication.md) variants).
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:::
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