CREATE OR REPLACE FUNCTION CHECK_SCHEDULE()
RETURNS TRIGGER AS
$BODY$
BEGIN
  IF EXISTS(
    SELECT DAY, TIME FROM MEETING
    WHERE NEW.DAY = MEETING.DAY AND NEW.TIME > MEETING.TIME
    ) THEN
    RAISE EXCEPTION 'THERE IS A MEETING HAPPENING ON % % ', NEW.DAY, NEW.TIME;
  ELSE
    RETURN NEW;
  END IF;
END;
$BODY$ LANGUAGE PLPGSQL;