UPDATE groups SET dom = NULL WHERE dom = 0;
UPDATE payments SET asso_id = NULL WHERE asso_id = 0;
UPDATE newsletter_art SET cid = NULL WHERE cid = 0;
+UPDATE newsletter_ins SET last = NULL WHERE last = 0;
-- Deletes things that should have been deleted ealier.
DELETE FROM newsletter_art WHERE NOT EXISTS (SELECT * FROM newsletter WHERE newsletter.id = newsletter_art.id);