<asp:DropDownList ID="DropDownList1" runat="server"
        DataSourceID="SqlDataSource1" DataTextField="track_user"
        DataValueField="track_user" Height="19px" Width="183px" AutoPostBack="True"
            onselectedindexchanged="DropDownList1_SelectedIndexChanged">
    </asp:DropDownList>
    <asp:SqlDataSource ID="SqlDataSource1" runat="server"
        ConnectionString="<%$ ConnectionStrings:MyDatabaseConnectionString %>"
        SelectCommand="SELECT DISTINCT [track_user] FROM [Track]">
    </asp:SqlDataSource>