text: 
  CREATE OR REPLACE FUNCTION display_message() RETURNS trigger AS $$
  	BEGIN
  		RAISE NOTICE 'ALTER TABLE ! %', TG_OP;
  		RETURN NULL;
  	END
  	$$ LANGUAGE plpgsql;
  
  CREATE TRIGGER t_test_avant
  	BEFORE INSERT or UPDATE or DELETE 
  	ON produit 
  	FOR EACH STATEMENT
  	EXECUTE PROCEDURE display_message();
  