ClickHouse/docs/en/sql-reference/statements/alter/statistics.md
2024-05-22 15:24:18 +02:00

34 lines
1.6 KiB
Markdown

---
slug: /en/sql-reference/statements/alter/statistics
sidebar_position: 45
sidebar_label: STATISTICS
---
# Manipulating Column Statistics
The following operations are available:
- `ALTER TABLE [db].table ADD STATISTICS (columns list) TYPE (type list)` - Adds statistic description to tables metadata.
- `ALTER TABLE [db].table MODIFY STATISTICS (columns list) TYPE (type list)` - Modifies statistic description to tables metadata.
- `ALTER TABLE [db].table DROP STATISTICS (columns 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 (columns 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 (columns list)` - Rebuilds the statistic for columns. Implemented as a [mutation](../../../sql-reference/statements/alter/index.md#mutations).
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.
There is an example adding two statistics types to two columns:
```
ALTER TABLE t1 MODIFY STATISTICS c, d TYPE TDigest, Uniq;
```
:::note
Statistic manipulation is supported only for tables with [`*MergeTree`](../../../engines/table-engines/mergetree-family/mergetree.md) engine (including [replicated](../../../engines/table-engines/mergetree-family/replication.md) variants).
:::