CREATE_EVENT_TRIGGER (7)

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

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 37, Event Triggers, in the documentation. The user who creates an event trigger becomes its owner.

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 37.1, “Overview of Event Trigger Behavior”, in the documentation 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.

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.

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 PROCEDURE abort_any_command();

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

ALTER EVENT TRIGGER (ALTER_EVENT_TRIGGER(7)), DROP EVENT TRIGGER (DROP_EVENT_TRIGGER(7)), CREATE FUNCTION (CREATE_FUNCTION(7))