grouping in gridview

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using MySql.Data.MySqlClient;
using System.Data;

namespace grisviewgrouping
{
    public partial class _Default : System.Web.UI.Page
    {
        MySqlConnection con = new MySqlConnection("Server=localhost;Database=projecttt;Uid=root;Pwd=xxxxxx;");

        protected void Page_Load(object sender, EventArgs e)
        {
           
        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            con.Open();
            MySqlCommand com = new MySqlCommand("select duration, toc from processeddata_table where dialdate BETWEEN ?sstart and ?sstop ", con);
            com.Parameters.Add("?sstart", MySqlDbType.Datetime).Value = TextBox1.Text;
            com.Parameters.Add("?sstop", MySqlDbType.Datetime).Value = TextBox2.Text;
            MySqlDataAdapter da = new MySqlDataAdapter(com);
            DataSet ds = new DataSet();
            da.Fill(ds);
            GridView1.DataSource = ds;
            GridView1.DataBind();
            con.Close();

        }
    }
}