访问和操作SQL server数据库中的数据

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim cn As New SqlConnection("Data Source=(local);Initial Catalog =northwind;Integrated Security=true")
        Dim da As New SqlDataAdapter
        Dim comselect As New SqlCommand("select productid,productname from product where categoryid=1", cn)
        Dim cominsert As New SqlCommand("instrt into products(productname) values(@productname)", cn)
        cominsert.Parameters.Add(New SqlParameter("@productname", SqlDbType.NVarChar, 40, ParameterDirection.Input, False, CType(0, Byte), CType(0, Byte), "productname", DataRowVersion.Current, Nothing))
        Dim comupdate As New SqlCommand("update products set productname=@productname where productid=@productid", cn)
        comupdate.Parameters.Add(New SqlParameter("@productname", SqlDbType.NVarChar, 40, ParameterDirection.Input, False, CType(0, Byte), CType(0, Byte), "productname", DataRowVersion.Current, Nothing))
        comupdate.Parameters.Add(New SqlParameter("@productid", SqlDbType.Int, 4, ParameterDirection.Input, False, CType(0, Byte), CType(0, Byte), "productid", DataRowVersion.Current, Nothing))        Dim comdelete As New SqlCommand("delete from product where productid=@productid", cn)
        comdelete.Parameters.Add(New SqlParameter("@productid", SqlDbType.Int, 4, ParameterDirection.Input, False, CType(0, Byte), CType(0, Byte), "productid", DataRowVersion.Current, Nothing))
        da.SelectCommand = comselect
        da.InsertCommand = cominsert
        da.UpdateCommand = comupdate
        da.DeleteCommand = comdelete
        Dim ds As New DataSet
        da.Fill(ds, "products")
        Dim i As Integer
        For i = 0 To ds.Tables(0).Rows.Count - 1
            Response.Write(ds.Tables(0).Rows(i).Item(1) & "br")
        Next i
        Dim row As DataRow = ds.Tables(0).NewRow()
        row.Item("productname") = "go juice"
        ds.Tables(0).Rows.Add(row)
        ds.Tables(0).Rows(0).Item("productname") = "good tea"
        Dim count As Integer = da.Update(ds, "products")
        ds.AcceptChanges()
        Response.Write("p" & count & "records affected..../p")
        For i = 0 To ds.Tables(0).Rows.Count - 1
            Response.Write(ds.Tables(0).Rows(i).Item(1) & "br")
        Next i 
    End Sub