SELECT ; cs.CustNo, ; cs.Customer, ; NVL(QtyIn, 000000), ; NVL(QtyOut, 000000), ; NVL(QtyIn, 000000)-NVL(QtyOut, 000000) As QtyDiff ; FROM Customer cs ; LEFT JOIN (SELECT cust, SUM(StandsIn) FROM StandsIn AS QtyIn GROUP BY 1) si ON si.cust = cs.custno ; LEFT JOIN (SELECT cust, SUM(SerialCnt) FROM Stands_Out AS QtyOut GROUP BY 1) so ON so.cust = cs.custno ; ORDER BY ; cs.Customer