>SELECT ;
>    CustNo, Customer, QtyIn, QtyOut, QtyIn-QtyOut As QtyDiff ;
>      FROM ( ;
>         SELECT ;
>            cs.CustNo, ;
>            cs.Customer, ;
>            SUM(si.StandsIn) AS QtyIn, ;
>            SUM(so.SerialCnt) As QtyOut ;
>               FROM Customer cs ;
>                  LEFT JOIN StandsIn si ON si.cust = cs.CustNo ;
>                  LEFT JOIN Stands_Out so ON so.cust = cs.CustNo ;
>               GROUP BY ;
>                  cs.CustNo, ;
>                  cs.Customer ;
>       ) dt1
>