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