CREATE EVENT TRIGGER

CREATE EVENT TRIGGER

CREATE EVENT TRIGGER

7

SQL - Language Statements

CREATE EVENT TRIGGER

define a new event trigger

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 ???. 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 ??? 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 ???) as well as when ??? is set to false. If an erroneous event trigger disables the database so much that you can't even drop the trigger, restart with ??? set to false to temporarily disable event triggers, or 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#