according to dropdown show multiple tables in a gridview in asp.net

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource1" AllowPaging="True" AllowSorting="True" AutoGenerateEditButton="True" DataKeyNames="pk_as_item_id">
<Columns>
<asp:BoundField ReadOnly="true" DataField="pk_as_item_id" HeaderText="ID" SortExpression="pk_as_item_id" />
<asp:BoundField DataField="description" HeaderText="Description" SortExpression="description" />
<asp:TemplateField HeaderText="Location" SortExpression="loca_description" >
<EditItemTemplate>
<asp:DropDownList ID="ddl_location" runat="server" DataSourceID="SqlDataSource2" DataValueField="pk_as_loca_id" DataTextField="loca_description" >
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="lbl_location" runat="server" Text='<%# Bind("loca_description") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>

<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:Personal %>"
SelectCommand="SELECT [pk_as_item_id], [description], [fk_as_loca_id], [pk_as_loca_id], [loca_description] FROM [ITEMS], [LOCATIONS] WHERE [fk_as_loca_id] = [pk_as_loca_id]"
UpdateCommand="UPDATE [ITEMS] SET [pk_as_item_id] = @pk_as_item_id, [description] = @description, [fk_as_loca_id] = ???????  WHERE [pk_as_item_id] = @pk_as_item_id">
</asp:SqlDataSource>

<asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:Personal %>"
SelectCommand="SELECT [pk_as_loca_id], [loca_description] FROM [LOCATIONS]">
</asp:SqlDataSource>