DropDowList problem

Question

Hi there, I need your help.
Here is my problem.


I have this DropDownList populate with this query in dbms SQL Server 2008:


            sql2 = "SELECT * FROM dbo_40 " +                        
                         " ORDER BY " +
                         " Sort;";
            dadapter = new SqlDataAdapter(sql2, ConnSqlServer);
            dset = new DataSet();
            dadapter.Fill(dset);
            DropDownList3.DataSource = dset.Tables[0];
            DropDownList3.DataTextField = "MAT";
            DropDownList3.DataValueField = "Sort";
            DropDownList3.DataBind();


In this DDL I need add the ALL value and tried this code:

<asp:DropDownList ID="DropDownList3" runat="server" AppendDataBoundItems="True" AutoPostBack="True"
                            Font-Size="10pt" OnSelectedIndexChanged="DropDownList3_SelectedIndexChanged">
                            <asp:ListItem Value="%">---</asp:ListItem>
                            <asp:ListItem Value="5">ALL</asp:ListItem>
                        </asp:DropDownList>




    public void GridViewBind()
    {
        sql1 = "SELECT TOP 1000 * FROM dbo_40;";




            if (DropDownList3.SelectedIndex == 5)
            {
                sql1 = "SELECT * FROM dbo_40 WHERE sID = 5;";
                Response.Write(DropDownList3.SelectedIndex);
            }


    }


    protected void DropDownList3_SelectedIndexChanged(object sender, EventArgs e)
    {
        GridViewBind();
    }

But in the code-behind the value DropDownList3.SelectedIndex for ALL it's null or empty.


Can you help me?
Thanks in advance.