C# Select ข้อมูลจาก table แรกเพื่อมา update อีก table นึงไม่ได้ครับ

 private void read_btn_Click(object sender, EventArgs e)
        {
            MySqlConnection conn = null;
            MySqlDataReader rdr = null;
            int count;
                DateTime time = DateTime.Now;
                string date_started = String.Format("{0:yyyy-MM-dd}", time);
                string time_started = String.Format("{0:HH:mm:ss}", time);

            try
            {

                conn = new MySqlConnection(ConnectionString);
                conn.Open();

                //อ่านค่า last_number จากตาราง queue_wait 
                string stm = "SELECT * FROM queue_wait ORDER BY time ASC LIMIT 1 ";
                MySqlCommand cmd_sel = new MySqlCommand(stm, conn);
                rdr = cmd_sel.ExecuteReader();
                

                if(rdr.Read())
                {
                    Console.WriteLine(rdr.GetString(1) + ": "
                        + rdr.GetString(2));
                    
                    last_number = int.Parse(rdr.GetString(2));

                }

                rdr.Close();  // ต้อง close ก่อนไม่งั้นจะมี error  There is already an open DataReader 

                //ตรวจสอบว่ามีข้อมูลอยู่แล้วหรือไม่
                string chk_data = "SELECT * FROM queue_data WHERE last_date = '" + date_started + "' LIMIT 1 ";
                MySqlCommand cmd_chk = new MySqlCommand(chk_data, conn);
                rdr = cmd_chk.ExecuteReader();
               

                if (rdr.Read())
                {
                    //ถ้ามีข้อมูลอยู่แล้วให้ update

                    count = int.Parse(rdr.GetString(2));
                    count += 1;
                    Console.WriteLine("count = " + count + ", last_number=" + last_number + ",last_time =" + time_started + ", last_date = " + date_started);


                    if (rdr != null)
                    {
                        rdr.Close();  // ต้อง close ก่อนไม่งั้นจะมี error  There is already an open DataReader 
                    } 

                    sql = "UPDATE queue_data SET count = " + count + ", last_number = " + last_number + ", last_time = " + time_started + ", status = false WHERE last_date ='" + date_started + "' ";

                    MySqlCommand cmd = new MySqlCommand(sql, conn);
                    cmd.ExecuteNonQuery();

                }
                else
                {
                    //ถ้าไม่มีข้อมูลให้ Insert

                }

              
            }
            catch (MySqlException ex)
            {
                Console.WriteLine("Error: {0}", ex.ToString());

            }
            finally
            {
                if (rdr != null)
                {
                    rdr.Close();
                }

                if (conn != null)
                {
                    conn.Close();
                }
            }