Hi Sean,
Thank you for your help. Now it works!

>
> I think you really want:
>
> IF (
> EXISTS( SELECT PERSONENID FROM ADRESSE
> WHERE
> -> (PERSONENID = NEW.PERSONENID) AND
> -> (ADRESSENTYP = NEW.ADRESSENTYP) AND
> -> ((GUELTIGVON IS NULL AND GUELTIGBIS IS
> NULL) OR
> (GUELTIGVON IS NULL AND
> NEW.GUELTIGVON IS NULL) OR
> -> (GUELTIGBIS IS NULL AND
> NEW.GUELTIGBIS IS NULL))
> )
> ) THEN
> EXCEPTION ADRESSE_UNGUELTIG;
>
> Sean
>