using System;

using System.Data;

using System.Xml;

using System.Collections.Generic;

using System.Linq;

using System.Data.DataSetExtensions;

public class Program

{

    public static void Main()

    {

                DataTable dt1 = new DataTable();

                dt1.Columns.Add("ID");

                dt1.Rows.Add(100);

                dt1.Rows.Add(200);

                dt1.Rows.Add(300);

​

                string MyStr = String.Join(",", dt1.AsEnumerable().Select(x => x.Field<string>("ID").ToString()).ToArray());

                Console.WriteLine(MyStr);

    }

}