PostgreSQL : Documentation: 10: CREATE EVENT TRIGGER : Postgres Professional

CREATE EVENT TRIGGER
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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 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 39. 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 39.1 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.

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 PROCEDURE abort_any_command();

Compatibility

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