NAME

       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 40. 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 40.1 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(1)). 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 (ALTER_EVENT_TRIGGER(7)), DROP EVENT TRIGGER (DROP_EVENT_TRIGGER(7)),
       CREATE FUNCTION (CREATE_FUNCTION(7))