CREATE EVENT TRIGGER

CREATE EVENT TRIGGER
Prev	Up	SQL Commands	Home	Next

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). 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. +