Autopopulating code (2-part) to pick the data from SQL- database

using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Data.SqlClient;
using System.Configuration;
using System.Text;

namespace Auto_WebService
{
  /// <summary>
  /// Summary description for Service1
  /// </summary>
  [WebService(Namespace = "http://webservices/")]
  [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
  [ToolboxItem(false)]
  public class Service1 : System.Web.Services.WebService
   {
    [WebMethod]
    public string GetListOfCountries()
     {
       SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["connection1"].ToString());
       con.Open();
       string str="select Name from AccountBase where len(isnull(name,'')) > 0";
       SqlDataAdapter da=new SqlDataAdapter(str,con);
       DataSet ds=new DataSet();
       da.Fill(ds);
       StringBuilder sb=new StringBuilder();
       for (int i = 0; i < ds.Tables[0].Rows.Count ; i++)
       {
          sb.Append(ds.Tables[0].Rows[i][0].ToString() + ",,");
       }
     //return string.Join(",,", arrayCountries);
     return sb.ToString();
     con.Close();
    //return "Hello World";
    }
  }
}