I created two parentgridview and childgridview .
<asp:GridView ID="ParentGridView" runat="server"
AutoGenerateColumns="False"
DataSourceID="SqlDataSource1" DataKeyNames="l_no"
onselectedindexchanged="ParentGridView_SelectedIndexChanged">
Columns>
<asp:TemplateField HeaderText="Letter Number">
<ItemTemplate>
<asp:Label id="l_no" Runat="Server"
Text='<%# Eval("l_no") %>'/>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="name Department">
<ItemTemplate>
<asp:Label id="nam_dep" Runat="Server"
Text='<%# Eval("nam_dep") %>'/>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="View">
<ItemTemplate>
<asp:Button ID="ViewChild_Button"
runat="server" Text="+" CommandName="Edit" />
</ItemTemplate>
<EditItemTemplate>
<asp:Button ID="CancelChild_Button"
runat="server" Text="-" CommandName="Cancel" />
</EditItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="<%$ ConnectionStrings:ABCConnectionString %>"
SelectCommand="SELECT * FROM [viewyn]"></asp:SqlDataSource>
<br />
<asp:SqlDataSource ID="SqlDataSource2" runat="server"
ConnectionString="<%$ ConnectionStrings:ABCConnectionString %>"
SelectCommand="SELECT * FROM [Letter_dept] WHERE ([l_no] = @l_no)">
<SelectParameters>
<asp:SessionParameter Name="l_no" SessionField="l_no" Type="String"/>
</SelectParameters>
</asp:SqlDataSource>where should i put anthor gridview where .
<asp:GridView ID="GrandChildGridView" runat="server"
AllowPaging="true" PageSize="4"
DataSourceID="SqlDataSource2">
</asp:GridView>protected void ParentGridView_OnRowEditing(object sender,GridViewEditEventArgs e)
{
int parent_index = e.NewEditIndex;
//to set the edit index of the Parent
//grid with that of the current row
ParentGridView.EditIndex = parent_index;
ParentGridView.DataBind();
//find the pubid_lbl containing pub_id in that
//particular row by using findcontrol method
GridViewRow row = ParentGridView.Rows[parent_index];
Label l_nu = (Label)row.FindControl("l_no");
//save pub_id and edit_index in session for childgridview's use
Session["l_no"] = l_nu.Text;
Session["ParentGridViewIndex"] = parent_index;
}