MySQL - AYUDA CON TRIGGER BEFORE UPDATE

CREATE TABLE `IDTPPD` ( `ID` char(2) COLLATE utf8_spanish_ci NOT NULL,

                        PRIMARY KEY (`ID`) )

CREATE TABLE `TPPDTO` ( `IDTP` char(2) COLLATE utf8_spanish_ci NOT NULL,

                        `CONCEPT` varchar(25) COLLATE utf8_spanish_ci NOT NULL,

                         PRIMARY KEY (`IDTP`) )

CREATE TRIGGER `BI_TPPDTO` BEFORE INSERT ON `TPPDTO`

FOR EACH ROW

  IF NEW.IDTP IS NULL THEN

    set NEW.IDTP = (SELECT IDTPPD.ID FROM IDTPPD order by ID limit 1);

  END IF

END

CREATE TRIGGER `BI_TPPDTO` BEFORE INSERT ON `TPPDTO`

FOR EACH ROW

  IF NEW.IDTP IS NULL THEN

    set NEW.IDTP = (SELECT IDTPPD.ID FROM IDTPPD order by ID limit 1);

  END IF

  DELETE FROM IDTPPD WHERE IDTPPD.ID = NEW.IDTP;

END