CREATE OR REPLACE TRIGGER Tr_Einbau BEFORE INSERT OR UPDATE ON Einbau
FOR EACH ROW
DECLARE Baugrp Bauteil.Baugruppe%TYPE := NULL;
BEGIN
IF INSERTING THEN
	SELECT Baugruppe INTO Baugrp FROM Bauteil WHERE Bauteil.BtNr = :new.BtNr;
	IF Baugrp =  NULL THEN
		SELECT sq_einbau.nextval INTO :new.EbNr FROM dual;
	ELSE
		RAISE_APPLICATION_ERROR (-20734,'Fehler');		
	END IF;
END IF;
IF UPDATING THEN
	:new.EbNr := :old.EbNr;
END IF;
END;
/