Calculated Column : DataColumn « ADO.net Database « ASP.NET Tutorial

<%@ Page language="c#" Inherits="CalculatedColumn" CodeFile="Default.aspx.cs" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
  <HEAD>
    <title>CalculatedColumn</title>
  </HEAD>
  <body>
    <form id="Form1" method="post" runat="server">
      <asp:GridView id="GridView1" runat="server"></asp:GridView>
    </form>
  </body>
</HTML>

File: Default.aspx.cs

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;


public partial class CalculatedColumn : System.Web.UI.Page
{

  protected void Page_Load(object sender, System.EventArgs e)
  {
    string connectionString = "Data Source=localhost;Initial Catalog=Northwind;Integrated Security=SSPI";
    SqlConnection con = new SqlConnection(connectionString);

    string sqlCat = "SELECT CategoryID, CategoryName FROM Categories";
    string sqlProd = "SELECT ProductName, CategoryID, UnitPrice FROM Products";

    SqlDataAdapter da = new SqlDataAdapter(sqlCat, con);
    DataSet ds = new DataSet();

    try
    {
      con.Open();
      da.Fill(ds, "Categories");

      da.SelectCommand.CommandText = sqlProd;
      da.Fill(ds, "Products");
    }
    finally
    {
      con.Close();
    }

    DataRelation relat = new DataRelation("CatProds",ds.Tables["Categories"].Columns["CategoryID"],ds.Tables["Products"].Columns["CategoryID"]);
    ds.Relations.Add(relat);

    DataColumn count = new DataColumn("Products (#)", typeof(int),"COUNT(Child(CatProds).CategoryID)");
    DataColumn max = new DataColumn("Most Expensive Product", typeof(decimal),"MAX(Child(CatProds).UnitPrice)");
    DataColumn min = new DataColumn("Least Expensive Product", typeof(decimal),"MIN(Child(CatProds).UnitPrice)");

    ds.Tables["Categories"].Columns.Add(count);
    ds.Tables["Categories"].Columns.Add(max);
    ds.Tables["Categories"].Columns.Add(min);

    GridView1.DataSource = ds.Tables["Categories"];
    GridView1.DataBind();
  }
}
18.23.DataColumn
	18.23.1.	Calculated Column