UPDATE vn.postCode pc
LEFT JOIN vn.zoneGeo zg ON zg.id = pc.geoFk
SET pc.geoFk = NULL
WHERE zg.id IS NULL;
ALTER TABLE vn.postCode
ADD CONSTRAINT postCode_zoneGeo_FK FOREIGN KEY (geoFk)
REFERENCES vn.zoneGeo(id)
ON DELETE RESTRICT
ON UPDATE CASCADE;