how to validate duplicate cell in each column in DGV

Question

 Design as in data grid view;

 Date      Period    CK  RK   MK Vk RK CMk VB GS MS TMS(STaff Name)

 7/1/2013  1         reo  reo(course)
 7/1/2013  2         PH2  REO


in the date(7/1/2013) for lst Period  reo should not come twice in the column.

for that how to avoid the duplicate,the  course name  (reo)  in data grid view.


please help me.  please send the code.for that duplication for course name (reo)