SELECT a1.paypal, a1.uid AS uid1, a2.uid AS uid2 FROM vms_auszahlungen a1 LEFT JOIN vms_auszahlungen a2 ON (a2.paypal = a1.paypal AND a2.uid != a1.uid) WHERE a1.art = "paypal" AND a2.paypal IS NOT NULL GROUP BY a1.paypal
So sieht meine Abfrage aus, mal so als Tipp