SQL Abfrage zusammenfassen?

[TBx]

sollte so funktionieren:

SQL-Code:

select 
  ((SELECT SUM(productbookingpos.quantity) FROM productbookingpos 
    WHERE productbookingpos.prod_ID = 111 
          AND productbookingpos.invalid =0) 
  -(SELECT SUM(invoicepos.quantity) FROM invoicepos 
    WHERE invoicepos.prod_ID = 111 
          AND invoicepos.invalid =0)) AS ERGEBNIS

Hope it helps

onlinekater