# ALTER FUNCTION

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

_(since v3.0.5)_

The `ALTER FUNCTION` statement can be used to modify an existing defined [function](/docs/reference/query-language/statements/define/function.md).

## Statement syntax

**SurrealQL Syntax**

```syntax title="SurrealQL Syntax"
ALTER FUNCTION [ IF EXISTS ] fn::@name
  [ ( [ $argument: @type, ... ] ) ] [ -> @type | DROP RETURNS ]
  [ { @query ... } ]
  [ COMMENT @string | DROP COMMENT ]
  [ PERMISSIONS [ NONE | FULL | WHERE @condition ] ] 
```

## Example usage

```surql
-- Declare a function
DEFINE FUNCTION fn::get_message($input: any) {
    $input.message
};

-- No `message` field, returns nothing
fn::get_message("wrong input");

-- Tighten up the valid input for the function
ALTER FUNCTION fn::get_message($input: { error_code: 200, message: string } | {error_code: 404, message: string} ) {
    $input.message
};

-- Returns an error now
fn::get_message("wrong input");

-- Okay, returns 'Looks good'
fn::get_message({ error_code: 200, message: "Looks good" });
```