CREATE EVENT TRIGGER — define a new event trigger
CREATE EVENT TRIGGERnameONevent[ WHENfilter_variableIN (filter_value[, ... ]) [ AND ... ] ] EXECUTE { FUNCTION | 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 38.  The user who creates an event trigger
   becomes its owner.
  
nameThe name to give the new trigger. This name must be unique within the database.
eventThe name of the event that triggers a call to the given function. See Section 38.1 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.
     
Only superusers can create event triggers.
   Event triggers are disabled in single-user mode (see postgres) as well as when
   event_triggers is set to false.
   If an erroneous event trigger disables the database so much that you can't
   even drop the trigger, restart with event_triggers
   set to false to temporarily disable event triggers, or
   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 FUNCTION abort_any_command();
   There is no CREATE EVENT TRIGGER statement in the
   SQL standard.