# ALTER TABLE

The ALTER TABLE statement is used to alter a defined table.

The `ALTER TABLE` statement is used to alter a defined table.

**SurrealQL Syntax**

```syntax title="SurrealQL Syntax"
ALTER TABLE [
	[ IF EXISTS ] @name
		[ DROP COMMENT ]
        [ DROP CHANGEFEED ]
        [ COMPACT ]
		[ SCHEMAFULL | SCHEMALESS ]
		[ PERMISSIONS [ NONE | FULL
			| FOR select @expression
			| FOR create @expression
			| FOR update @expression
			| FOR delete @expression
		] ]
    [ CHANGEFEED @duration ]
    [ COMMENT @string ] 
    [ CHANGEFEED ]
]
```

## COMPACT

_(since v3.0.0)_

Performs storage compaction on a specific table keyspace. To compact other resources, use [ALTER SYSTEM](/docs/reference/query-language/statements/alter/system.md) to compact the entire datastore, [ALTER NAMESPACE](/docs/reference/query-language/statements/alter/namespace.md) to compact the current namespace keyspace, or [ALTER DATABASE](/docs/reference/query-language/statements/alter/database.md) to compact the current database keyspace.

The actual compaction used will depend on the datastore, such as RocksDB or SurrealKV.

This clause will not work with in-memory storage which has nothing persistent to compact, producing the following error:

```surql
'The storage layer does not support compaction requests.'
```

A successful compaction will return `NONE`.

```surql
ALTER TABLE user COMPACT;
-- NONE
```

## See also

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