> ## Documentation Index
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> Documentation for Manipulating Data Skipping Indices

# Manipulating Data Skipping Indices

The following operations are available:

<h2 id="add-index">
  ADD INDEX
</h2>

`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.

<h2 id="drop-index">
  DROP INDEX
</h2>

`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](/reference/statements/alter/index#mutations).

<h2 id="materialize-index">
  MATERIALIZE INDEX
</h2>

`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](/reference/statements/alter/index#mutations). If `IN PARTITION` part is omitted then it rebuilds the index for the whole table data.

<h2 id="clear-index">
  CLEAR INDEX
</h2>

`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](/reference/statements/alter/index#mutations).

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`](/reference/engines/table-engines/mergetree-family/mergetree) engine (including [replicated](/reference/engines/table-engines/mergetree-family/replication) variants).
</Note>