VB.NET รบกวนพี่ๆหน่อยค่า ช่วยเขียนฟังก์ชั่น คิดส่วนลดจากโปรโมชั่น ซึ่งมีสองเงื่อนไขคือใช้ ราคาหา กับใช้ จำนวนชิ้นหา

 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click



        Dim product_code As String = product.SelectedItem.Value
        Dim price As Decimal = txt_price.Text
        Dim unit As Decimal = txt_NumProduct.Text
        Dim PriceIncludes As Decimal = price * unit
     Dim dis As String = Calculate(product_code, PriceIncludes, unit)
            Dim total As Decimal = PriceIncludes - dis
            price = (Math.Truncate(price * 100)) / 100

            If IsNumeric(txt_price.Text) Then
                TextBox2.Text = ("" & PriceIncludes)
                TextBox3.Text = (" " & dis)
                TextBox4.Text = (" " & total)

     
        End If


    End Sub

Function Calculate(ByVal product_code As String, ByVal PriceIncludes As Decimal, ByVal Unit As Decimal) As Decimal


        Dim dis As Decimal = 0
        Dim dt As New DataTable
        Dim sqlconn As New OleDbConnection(ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString)
        Dim reader As OleDbDataReader
        Dim comm As New StringBuilder
        comm.Append(" select discount ")
        comm.Append(" from promotion ")
        comm.Append(" where product = ? ")
        comm.Append(" and ( ( minmax_type_id = '2' and ((min_price <=  ? )  and  (isnull(max_price,9999999 ) >=  ?)))")
        comm.Append(" or( minmax_type_id = '1' and ((min_price <=   ? )  and  (isnull(max_price,9999999 ) >= ?)) ) ) ")


        Dim OleComm As New OleDbCommand(comm.ToString, sqlconn)
        OleComm.Parameters.AddWithValue("@00", product_code)
        OleComm.Parameters.AddWithValue("@01", PriceIncludes)
        OleComm.Parameters.AddWithValue("@02", PriceIncludes)
        OleComm.Parameters.AddWithValue("@03", Unit)
        OleComm.Parameters.AddWithValue("@04", Unit)


        sqlconn.Open()
        reader = OleComm.ExecuteReader(CommandBehavior.CloseConnection)
        If reader.HasRows Then
            dt.Load(reader)
            dis = dt.Rows(0).Item("discount")
        End If
        'Dim a As New Page4
        'a.MinMax()


        Return dis


    End Function