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ClickHouse/docs/en/sql-reference/statements/alter/index/index.md
Ivan Blinkov ffe2cecb1b
[docs] split the ALTER article (#12502) 
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true 42 INDEX

Manipulating Data Skipping Indices

The following operations are available:

  • ALTER TABLE [db].name ADD INDEX name expression TYPE type GRANULARITY value AFTER name [AFTER name2] - Adds index description to tables metadata.

  • ALTER TABLE [db].name DROP INDEX name - Removes index description from tables metadata and deletes index files from disk.

  • ALTER TABLE [db.]table MATERIALIZE INDEX name IN PARTITION partition_name - The query rebuilds the secondary index name in the partition partition_name. Implemented as a mutation.

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

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

!!! note "Note" Index manipulation is supported only for tables with *MergeTree engine (including replicated variants).