DataSet and DataAdapter

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            SqlConnection conn = new SqlConnection("Server=zhuobin;uid=sa;pwd=zhuobin;database=Northwind");
            String sql = @"select productname,unitprice from products where unitprice<20 and productname='Chai'";
            try
            {
                conn.Open();
                SqlDataAdapter da = new SqlDataAdapter(sql,conn);
                DataSet ds = new DataSet();
                da.Fill(ds,"products");
                DataTable dt=ds.Tables["products"];
                //display data
                foreach (DataRow row in dt.Rows)
                {
                    Console.WriteLine("The row is "+row.ToString());
                    Console.WriteLine(dt.Rows.Count.ToString());
                    foreach (DataColumn col in dt.Columns)
                    {
                        Console.WriteLine(row[col]);//mean that rows["productname"]
                        Console.WriteLine("The column is "+col.ToString());//output the field!
                    } Console.WriteLine("".PadLeft(20,'='));
                }
                
            }
            catch (SqlException ex)
            {
                Console.WriteLine("Error:{0}", ex.Message);
            }
            finally
            {
                conn.Close();
            }
            Console.ReadLine();
        }
    }
}