John's way will work great. Another way to accomplish this using joins is:

CurrentMonth = 9
CurrentYear = 2000

SELECT clientid ;
FROM clients    ;
INNER JOIN Payments ON Clients.ClientID = Payments.ClientID ;
WHERE Payments.Month == CurrentMonth AND Payments.Year == CurrentYear         ;

>Hi all,
>
>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 ?