CREATE EVENT TRIGGER — define a new event trigger
CREATE EVENT TRIGGERnameONevent[ WHENfilter_variableIN (filter_value[, ... ]) [ AND ... ] ] EXECUTE PROCEDUREfunction_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 39.  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 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.
     
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.
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();
   There is no CREATE EVENT TRIGGER statement in the
   SQL standard.