CREATE OR REPLACE FUNCTION update_datemodified_column()	
RETURNS TRIGGER AS $$
BEGIN
IF TG_OP = 'INSERT' THEN
           new.datemodified=now();
            RETURN NEW;
               ELSIF TG_OP = 'UPDATE' THEN
                       new.datemodified= now();
            RETURN NEW;
        ELSE
            RETURN old;
        END IF;
END;
$$ language 'plpgsql';
DROP TRIGGER IF EXISTS update_datemodified ON roads.highways;
CREATE TRIGGER update_datemodified before insert or update ON roads.highways FOR EACH ROW EXECUTE PROCEDURE  update_datemodified_column();