# 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 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.