CurrentMonth = 9
CurrentYear = 2000

SELECT ClientId ;
   FROM Clients    ;
   INNER JOIN Payments ON Clients.ClientID = Payments.ClientID ;
   WHERE Payments.Month == CurrentMonth ;
   AND Payments.Year == CurrentYear ;
   AND ISNULL(Payments.Amount) ;
   OR {Amount due from some other table?} > Payments.Amount 




>>>I have two tables, both are relationed,(one-to-many).One contains clients and the other payments.Now, how can I search clients that haven´t yet paid in the current month and in the current year the monthly fee ?