ASP spul

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Configuration;
using System.Data.SqlClient;
namespace aspsite.application
{
    public partial class Default : System.Web.UI.Page
    {
        SqlConnection conNorthwind = new SqlConnection();
        SqlCommand comKlanten = new SqlCommand();
        SqlCommand comKlantIDs = new SqlCommand();
        SqlCommand comOrders = new SqlCommand();
        SqlDataAdapter daKlanten = new SqlDataAdapter();
        DataSet dsKlanten = new DataSet();
        DataTable dtKlanten = new DataTable("klanten");
        DataTable dtOrders = new DataTable("orders");
        SqlDataReader drKlantIDs;
        protected void Page_Load(object sender, EventArgs e)
        {
            conNorthwind.ConnectionString = ConfigurationManager.ConnectionStrings["NorthwindConnectionstring"].ConnectionString;
            comKlanten.Connection = conNorthwind;
            comOrders.Connection = conNorthwind;
            comKlanten.CommandText = "SELECT * FROM Customers";
            comKlantIDs.Connection = conNorthwind;
            comKlantIDs.CommandText = "SELECT customerid FROM customers ORDER BY customerid";
            daKlanten.SelectCommand = comKlanten;
            dsKlanten.Tables.Add(dtKlanten);

            daKlanten.Fill(dsKlanten.Tables["klanten"]);
            gvKlanten.DataSource = dsKlanten.Tables["klanten"];
            gvKlanten.DataBind();


            if (!IsPostBack)
            {

                conNorthwind.Open();
                drKlantIDs = comKlantIDs.ExecuteReader();
                while (drKlantIDs.Read())
                {
                    ddKlantIDs.Items.Add(drKlantIDs.GetValue(0).ToString());
                }
                conNorthwind.Close();

            }

            /* DataSet dsAgenda = new DataSet("agenda");
            DataTable dtAfspraak = new DataTable("afspraak");
            DataColumn dcdatum = new DataColumn("datum");
            DataColumn dctijd = new DataColumn("tijd");
            DataColumn dcwaar = new DataColumn("waar");
            DataColumn dcwie = new DataColumn("wie");


            dtAfspraak.Columns.Add(dcdatum);
            dtAfspraak.Columns.Add(dctijd);
            dtAfspraak.Columns.Add(dcwaar);
            dtAfspraak.Columns.Add(dcwie);

            dsAgenda.Tables.Add(dtAfspraak);

            string pad = Server.MapPath(@"~\xml\agenda.xml");
            dsAgenda.ReadXml(pad);

            gvAgenda.DataSource = dsAgenda.Tables["agenda"];
            gvAgenda.DataBind();
            */



        }

        protected void btnVerzend_Click(object sender, EventArgs e)
        {
            comOrders.Connection = conNorthwind;
            comOrders.CommandText = @"SELECT Products.ProductID,Products.ProductName,
                                            [Order Details].Quantity,
                                                CAST([Order Details].UnitPrice as DECIMAL(5,2)) as Stuksprijs,
                                                CAST([Order Details].Quantity*[Order Details].UnitPrice as DECIMAL(10,2) as Regeltotaal),
                                                FROM Orders,[Order Details].Products
                                                WHERE Orders.OrderID=[Order Details].OrderID
                                                AND Products.ProductID = [Order Details].ProductID
                                                AND Orders.CustomerID=@klantID";
            comOrders.Parameters.Add("@klantID", SqlDbType.NChar);
            comOrders.Parameters["@klantID"].Value = ddKlantIDs.Text;
            daKlanten.SelectCommand = comOrders;
            daKlanten.Fill(dsKlanten.Tables["orders"]);
            gvKlanten.DataSource = dsKlanten.Tables["orders"];


        }
    }
}