how we dispaly data in grid view from sql server

on button click event
                 {
                  con.Open();//connection open
                  SqlCommand cmd = new SqlCommand("Select * from tablename", con);

                 // SqlCommand cmd = new SqlCommand(hidSelectedText.Value, con);
                  SqlDataAdapter da = new SqlDataAdapter(cmd);
                  DataTable dt = new DataTable();
                  da.Fill(dt);
                  GridView1.DataSource = dt;
                  GridView1.DataBind();
                  con.Close();
                  }