Gridview updating rows for two tables

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C#

ASP.NET

Hi
I am trying to update the gridview row but its not working.Because I have rows from two different tables whick i have joined. But the second column is not updating. Please help.
here is my code

<asp:GridView ID="gvProducts" runat="server" AutoGenerateEditButton="True" AutoGenerateColumns="False"
                OnRowEditing="gvProducts_RowEditing" 
            OnRowUpdating="gvProducts_RowUpdating" CellPadding="1"
                ForeColor="#333333" GridLines="None" DataSourceID="SqlDataSource1" 
            Height="75px" Width="660px" DataKeyNames="BranchCode" AllowPaging="True" 
            PageSize="20">
                <rowstyle backcolor="#EFF3FB" />
                <columns>
                    <asp:BoundField DataField="BranchCode" HeaderText="BranchCode" ReadOnly="True" 
                        SortExpression="BranchCode" />
                    <asp:BoundField DataField="BranchName" HeaderText="BranchName" 
                        SortExpression="BranchName" />
                    <%--<asp:BoundField DataField="TierName" HeaderText="Branch Group" 
                        SortExpression="TierName" />  --%>
                    
                    <asp:TemplateField HeaderText="Branchgroup">
                    <edititemtemplate>
                        <asp:DropDownList ID="DropDownList1" runat="server" AppendDataBoundItems="True" DataSourceID="SqlDataSource1" DataTextField="TierName" DataValueField="TierName" Width="120px" Height="25px" >
                    </edititemtemplate>
                    <itemtemplate>
                    <asp:Label ID="Label1" runat="server" Text='<%# Bind("TierName") %>'>
                    </itemtemplate>
                </columns>
                <editrowstyle backcolor="#2461BF" />
                <footerstyle backcolor="#507CD1" font-bold="True" forecolor="White" />
                <pagersettings firstpagetext="First</br>" lastpagetext="Last </br>">
                    Mode="NextPrevious" NextPageText="Next</br>" 
                    PreviousPageText="Previous </br>" />
                <pagerstyle backcolor="#2461BF" forecolor="White" horizontalalign="Center" />
                <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
                <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" 
                    HorizontalAlign="Left" />
                <alternatingrowstyle backcolor="White" />
                <sortedascendingcellstyle backcolor="#F5F7FB" />
                <sortedascendingheaderstyle backcolor="#6D95E1" />
                <sorteddescendingcellstyle backcolor="#E9EBEF" />
                <sorteddescendingheaderstyle backcolor="#4870BE" />
            
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" 
            ConnectionString="<%$ %>"                                   
            SelectCommand="SELECT Admin_Branch.BranchCode, Admin_Branch.BranchName, Admin_Tier.TierName FROM Admin_Branch INNER JOIN Admin_Tier ON Admin_Branch.TierCode = Admin_Branch.TierCode"
             UpdateCommand="UPDATE Admin_Branch set BranchName=@BranchName where BranchCode=@BranchCode">
        </pagersettings>