# ALTER FIELD

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

The `ALTER FIELD` statement is used to change or entirely drop clauses of a defined field on a table.

## Statement syntax

**SurrealQL Syntax**

```syntax title="SurrealQL Syntax"
ALTER FIELD [ IF EXISTS ] ON [ TABLE ] @table 
[ 
    DROP TYPE |
    DROP FLEXIBLE |
    DROP READONLY |
    DROP VALUE |
    DROP ASSERT |
    DROP DEFAULT |
    DROP COMMENT |
    DROP REFERENCE |
    FLEXIBLE |
    READONLY |
    REFERENCE |
    TYPE @type |
    VALUE @value |
    ASSERT @expression |
    DEFAULT [ ALWAYS ] @expression |
    [ PERMISSIONS [ NONE | FULL
		| FOR select @expression
		| FOR create @expression
		| FOR update @expression
		| FOR delete @expression
	] ]
    COMMENT @string |
]
```

## Examples

As `ALTER FIELD` contains the same clauses available in a [`DEFINE FIELD`](/docs/reference/query-language/statements/define/field.md) statement, be sure to see that page for more examples.

Here is one example in which the `name` field is defined for a record `user`:

```surql
DEFINE FIELD name ON user TYPE string;
```

Later on, a database-wide [parameter](/docs/reference/query-language/statements/define/param.md) is defined to disallow certain user names. This can be followed up with an `ALTER FIELD` statement to add the `ASSERT` clause to it.

```surql
DEFINE PARAM $DISALLOWED_NAMES VALUE ["Lord British", "Lord Blackthorn"];
ALTER FIELD name ON user ASSERT $value NOT IN $DISALLOWED_NAMES;
CREATE user SET name = "Lord British";
```

```surql title="Output"
"Found 'Lord British' for field `name`, with record `user:yn4yttkg5w683q2937bq`, but field must conform to: $value NOTINSIDE $DISALLOWED_NAMES""
```

## See also

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