MySQL UPDATE BEFORE trigger puzzler
FOR EACH ROW
BEGIN

 IF NEW.IsDirty = 0 AND OLD.IsDirty=1 THEN
  SET NEW.IsDirty = 0;
 ELSE SET NEW.IsDirty = 1;
 END IF;

END;

FOR EACH ROW
BEGIN

IF NEW.IsDirty = 0 AND OLD.IsDirty=1 THEN
 SET NEW.IsDirty = 0;
ELSEIF NEW.IsDirty = 0 AND OLD.IsDirty=0 THEN
 SET NEW.IsDirty = 0;
ELSE SET NEW.IsDirty = 1;
END IF;

BEGIN
  SET NEW.EffectiveDate = current_timestamp;
  IF NEW.IsDirty = -1 THEN
    BEGIN
      SET NEW.IsDirty = 0;
    END;
  ELSE
    SET NEW.IsDirty = 1;
  END IF;
END

UPDATE task_set SET IsDirty = -1 WHERE CategoryID = 20