ClickHouse/docs/en/sql-reference/statements/alter/skipping-index.md

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/en/sql-reference/statements/alter/skipping-index	true	42	INDEX

Manipulating Data Skipping Indices

The following operations are available:

ADD INDEX

ALTER TABLE [db.]table_name [ON CLUSTER cluster] ADD INDEX [IF NOT EXISTS] name expression TYPE type [GRANULARITY value] [FIRST|AFTER name] - Adds index description to tables metadata.

DROP INDEX

ALTER TABLE [db.]table_name [ON CLUSTER cluster] DROP INDEX [IF EXISTS] name - Removes index description from tables metadata and deletes index files from disk. Implemented as a mutation.

MATERIALIZE INDEX

ALTER TABLE [db.]table_name [ON CLUSTER cluster] MATERIALIZE INDEX [IF EXISTS] name [IN PARTITION partition_name] - Rebuilds the secondary index name for the specified partition_name. Implemented as a mutation. If IN PARTITION part is omitted then it rebuilds the index for the whole table data.

CLEAR INDEX

ALTER TABLE [db.]table_name [ON CLUSTER cluster] CLEAR INDEX [IF EXISTS] name [IN PARTITION partition_name] - Deletes the secondary index files from disk without removing description. Implemented as a mutation.

The commands ADD, DROP, and CLEAR are lightweight in the sense that they only change metadata or remove files. Also, they are replicated, syncing indices metadata via ClickHouse Keeper or ZooKeeper.

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