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 a 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). :::