# ALTER INDEX

The ALTER statement can be used to change authentication access and behaviour, global parameters, table configurations, table events, schema definitions, and indexes.

_(since v3.0.0)_

The `ALTER INDEX` statement is used to alter a defined index on a table.

**SurrealQL Syntax**

```syntax title="SurrealQL Syntax"
ALTER INDEX @name ON TABLE @table
    COMMENT @string |
    PREPARE REMOVE |
    DROP COMMENT
```

## `PREPARE REMOVE` clause

As the name implies, an `ALTER INDEX PREPARE REMOVE` statement alters an index to prepare it for removal. This statement sets up a step in which the index has been decommissioned (prepared for removal), but not yet removed. At this point, `SELECT` queries along with the `EXPLAIN` clause to monitor query performance without the index.

```surql
-- 1. Decommission the index
ALTER INDEX my_index ON my_table PREPARE REMOVE;

-- 2. Monitor query performance and verify queries still work
SELECT ... FROM my_table EXPLAIN;

-- 3. If satisfied, permanently remove the index
REMOVE INDEX my_index ON my_table;
```

If removing the index is no longer desired, it can be restored to a useful state by using a [REBUILD INDEX](/docs/reference/query-language/statements/rebuild.md) statement.

```surql
REBUILD INDEX my_index ON my_table;
```

## See also

* [`DEFINE INDEX`](/docs/reference/query-language/statements/define/indexes.md)