Have u created the datagrid at runtime? If u have not , there is no need to specify the function name
OnpageIndexedChange = "DataGrid1_PageIndexChanged"
Just code ur pageindex functionality on the "Datagrid"_pageindexchanged function. That is provided to u default.
u can add the items to combo box with the value along with items. So that it will help in ceating linking between database table field. This can be done by adding item to combo box as listitem. The combo box item's value can be directly map to key feild of database table.