on behalf of this article :
http://codedisplay.com/show-grand-total-running-total-sub-total-in-asp-net-gridview-footer-c-vb-net/
lets assume i have four columns
| Sr | Company | Date | Billing amount | 
| 1 | Imtiaz Super Market | 11/12/1991 | 2000 | 
| 2 | Naheed mart | 11/12/1991 | 4000 | 
| 3 | Imtiaz Super Market | 11/12/1991 | 3000 | 
now it must group by the company name and show running total and net total like :
| Sr | Company | Date | Billing amount | 
| 1 | Imtiaz Super Market | 11/12/1991 | 2000 | 
| 2 | Imtiaz Super Market | 11/12/1991 | 3000 | 
|  |  |  | 5000 | 
| 3 | Naheed mart | 11/12/1991 | 4000 | 
| 4 | Naheed mart | 11/12/1991 | 5000 | 
|  |  |  | 9000 | 
|  |  |  | 14000 | 
NOTE : it must support paging and must be binded with data table