bubbling in asp.net with two checkboxes

protected void chkall_CheckedChanged(object sender, EventArgs e)
        {
            foreach (GridViewRow row in GridView1.Rows)
            {
        CheckBox chksingle = (CheckBox)row.Cells[0].FindControl("chksingle");
         chksingle.Checked =  ((CheckBox)sender).Checked;
         }
      }


      void DBind()
        {
     con = new SqlConnection("server=.;database=shikhar;integrated security=true");
     adap = new SqlDataAdapter("select * from emp", con);
     ds = new DataSet();
     adap.Fill(ds, "emp");
     GridView2.DataSource = ds.Tables[0];
     GridView2.DataBind();
     con.Close();
      }


        protected void Button2_Click(object sender, EventArgs e)
        {
 SqlConnection con = new SqlConnection("server=.;database=shikhar;integrated security=true");
      con.Open();
      foreach (GridViewRow row in GridView2.Rows)
            {
   CheckBox chksingle = row.Cells[0].FindControl("chksingle") as CheckBox;
             if (chksingle.Checked)
                {
  SqlCommand cmd = new SqlCommand("delete employee where id='"+row.Cells[1].Text+"'",con);
              
                    cmd.ExecuteNonQuery();
                }
            }
            con.Close();
            con.Dispose();
            DBind();
        }
    }