[NumLock]

нужно на этапе проектирования встать на свойство MasterFields и нажать F1, посмотреть MasterSource, MasterFields example:

Suppose you have a master table named Customer that contains a CustNo field. You also have a data source component named CustSource whose DataSet property specifies the Customer table. Finally, you have a detail table named Orders that also has a CustNo field. To display only those records in Orders that have the same CustNo value as the current record in Customer, write this code:

Orders.MasterSource := CustSource;

Orders.MasterFields := 'CustNo';

If you want to display only the records in the detail table that match more than one field value in the master table, specify each field and separate them with a semicolon.

Orders.MasterFields := 'CustNo;SaleDate';