## CREATE EVENT TRIGGER

CREATE EVENT TRIGGER — define a new event trigger

## Synopsis

    CREATE EVENT TRIGGER name
        ON event
        [ WHEN filter_variable IN (filter_value [, ... ]) [ AND ... ] ]
        EXECUTE { FUNCTION | PROCEDURE } function_name()

## Description

`CREATE EVENT TRIGGER` creates a new event trigger. Whenever the designated event occurs and the `WHEN` condition associated with the trigger, if any, is satisfied, the trigger function will be executed. For a general introduction to event triggers, see Chapter 39. The user who creates an event trigger becomes its owner.

## Parameters

`name`

  The name to give the new trigger. This name must be unique within the database.

`event`

  The name of the event that triggers a call to the given function. See Section 39.1 for more information on event names.

`filter_variable`

  The name of a variable used to filter events. This makes it possible to restrict the firing of the trigger to a subset of the cases in which it is supported. Currently the only supported `filter_variable` is `TAG`.

`filter_value`

  A list of values for the associated `filter_variable` for which the trigger should fire. For `TAG`, this means a list of command tags (e.g. `'DROP FUNCTION'`).

`function_name`

  A user-supplied function that is declared as taking no argument and returning type `event_trigger`.

  In the syntax of `CREATE EVENT TRIGGER`, the keywords `FUNCTION` and `PROCEDURE` are equivalent, but the referenced function must in any case be a function, not a procedure. The use of the keyword `PROCEDURE` here is historical and deprecated.

## Notes

Only superusers can create event triggers.

Event triggers are disabled in single-user mode (see postgres). If an erroneous event trigger disables the database so much that you can't even drop the trigger, restart in single-user mode and you'll be able to do that.

## Examples

Forbid the execution of any DDL command:

    CREATE OR REPLACE FUNCTION abort_any_command()
      RETURNS event_trigger
     LANGUAGE plpgsql
      AS $$
    BEGIN
      RAISE EXCEPTION 'command % is disabled', tg_tag;
    END;
    $$;

    CREATE EVENT TRIGGER abort_ddl ON ddl_command_start
       EXECUTE FUNCTION abort_any_command();

## Compatibility

There is no `CREATE EVENT TRIGGER` statement in the SQL standard.

## See Also

ALTER EVENT TRIGGER, DROP EVENT TRIGGER, CREATE FUNCTION