SqlConnection conn = new SqlConnection("Data Source=****;Initial Catalog=****;User ID=***;Password=****");
            conn.Open();
            SqlCommand cmd = conn.CreateCommand();
            SqlTransaction transaction = conn.BeginTransaction(); //開始事務
         try
            {

                cmd.Connection 
 
= conn;
                cmd.Transaction = transaction;
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = " select * from prediction_group   (xlock)  where prediction_date_ID=@prediction_date_ID";
                cmd.Parameters.AddWithValue("@prediction_date_ID", 4
 
);

                SqlDataReader reader2 = cmd.ExecuteReader();
                reader2.Read();
                string sample2 = reader2["sample2"].ToString();
                reader2.Close();

                cmd.CommandText = "update   prediction_group  set sample2 = '" + sample2 + "' WHERE ID =@ID
 
";
                cmd.Parameters.AddWithValue("@ID", 4);
                cmd.Parameters.AddWithValue("@sample2", 4);
                cmd.ExecuteNonQuery();

                transaction.Commit(); //事務完成之後提交事務



            }
            catch (Exception ex)
            {
                transaction.Rollback(); //如果事務沒有完成，就回滾事務

                throw;
            }
            finally
            {
                conn.Close();

            }