Hi各位大老，下列問題我實際上已經用別的寫法解決，
但我還是想問一下關於下列程式碼是哪裡出問題？
我看我設置的reader都有關閉，但是卻一直跳錯誤。
都是在updateStageCommand.ExecuteNonQuery();這條出現(X)
訊息：
System.InvalidOperationException: 'There is already an open DataReader associated with this Connection which must be closed first.'
程式要達成的目標是：
當我刪除任一筆資料時，如果同個uid中有stage
大於要刪除的stage，那麼大於的部分都要-1
資料修正前(移除a2)：
rid：a1、uid：ariel、stage：1
rid：a2、uid：ariel、stage：2
rid：a3、uid：ariel、stage：3
rid：a4、uid：ariel、stage：4
資料修正後：
rid：a1、uid：ariel、stage：1
rid：a3、uid：ariel、stage：2
rid：a4、uid：ariel、stage：3

我有兩種寫法，一開始只有用前端抓取rid。然後到資料庫操作。

public void DeletePoSignById(string rid)
        {
            SqlConnection sqlConnection = new SqlConnection(ConnStr);
            SqlCommand sqlCommand = new SqlCommand("SELECT uid, stage FROM Po_sign WHERE rid = @rid");
            sqlCommand.Connection = sqlConnection;
            sqlCommand.Parameters.Add(new SqlParameter("@rid", rid));
            sqlConnection.Open();
            SqlDataReader reader = sqlCommand.ExecuteReader();
            string uid = "";
            int stage = 0;
            if (reader.Read())
            {
                uid = Convert.ToString(reader["uid"]);
                stage = Convert.ToInt32(reader["stage"]);
            }
            reader.Close();

            sqlCommand = new SqlCommand("SELECT * FROM Po_sign WHERE uid = @uid");
            sqlCommand.Connection = sqlConnection;
            sqlCommand.Parameters.Add(new SqlParameter("@uid", uid));
            SqlDataReader relatedReader = sqlCommand.ExecuteReader();
            bool hasHigherStage = false;
            while (relatedReader.Read())
            {
                int relatedStage = Convert.ToInt32(relatedReader["stage"]);
                if (relatedStage > stage)
                {
                    hasHigherStage = true;
                    int updatedStage = relatedStage - 1;
                    SqlCommand updateStageCommand = new SqlCommand("UPDATE Po_sign SET stage = @updatedStage WHERE uid = @uid AND stage = @relatedStage");
                    updateStageCommand.Connection = sqlConnection;
                    updateStageCommand.Parameters.Add(new SqlParameter("@updatedStage", updatedStage));
                    updateStageCommand.Parameters.Add(new SqlParameter("@uid", uid));
                    updateStageCommand.Parameters.Add(new SqlParameter("@relatedStage", relatedStage));
                    updateStageCommand.ExecuteNonQuery();
                }
            }
            relatedReader.Dispose();
            if (!hasHigherStage)
            {
                sqlCommand = new SqlCommand("DELETE FROM Po_sign WHERE rid = @rid");
                sqlCommand.Connection = sqlConnection;
                sqlCommand.Parameters.Add(new SqlParameter("@rid", rid));
                sqlCommand.ExecuteNonQuery();
            }
            sqlConnection.Close();
        }

第二種寫法是 再從前端多抓些資料過來操作，但還是一樣問題：

public void DeletePoSignById(string rid,string uid,int stage)
        {
            SqlConnection sqlConnection = new SqlConnection(ConnStr);
            sqlConnection.Open();

            SqlCommand sqlCommand = new SqlCommand("SELECT * FROM Po_sign WHERE uid = @uid");
            sqlCommand.Connection = sqlConnection;
            sqlCommand.Parameters.Add(new SqlParameter("@uid", uid));

            SqlDataReader relatedReader = sqlCommand.ExecuteReader();
            bool hasHigherStage = false;
            while (relatedReader.Read())
            {
                int relatedStage = Convert.ToInt32(relatedReader["stage"]);
                if (relatedStage > stage)
                {
                    hasHigherStage = true;
                    int updatedStage = relatedStage - 1;
                    SqlCommand updateStageCommand = new SqlCommand("UPDATE Po_sign SET stage = @updatedStage WHERE uid = @uid AND stage = @relatedStage");
                    updateStageCommand.Connection = sqlConnection;
                    updateStageCommand.Parameters.Add(new SqlParameter("@updatedStage", updatedStage));
                    updateStageCommand.Parameters.Add(new SqlParameter("@uid", uid));
                    updateStageCommand.Parameters.Add(new SqlParameter("@relatedStage", relatedStage));
                    updateStageCommand.ExecuteNonQuery();
                }
            }
            relatedReader.Dispose();
            if (!hasHigherStage)
            {
                sqlCommand = new SqlCommand("DELETE FROM Po_sign WHERE rid = @rid");
                sqlCommand.Connection = sqlConnection;
                sqlCommand.Parameters.Add(new SqlParameter("@rid", rid));
                sqlCommand.ExecuteNonQuery();
            }
            sqlConnection.Close();
        }

最後我是用下列程式解決問題；
但因為是直接換寫法，所以上面的問題我還是不懂哪裡有誤！

        public void DeletePoSignById(string rid, string uid, int stage)
        {
            SqlConnection sqlConnection = new SqlConnection(ConnStr);
            sqlConnection.Open();
            SqlCommand sqlCommand = new SqlCommand(
                " DECLARE @tmp TABLE (rid varchar(50)) " +
                " INSERT INTO @tmp " +
                " SELECT rid FROM Po_sign WHERE uid = @uid And stage > @stage " +
                " WHILE EXISTS(SELECT rid FROM @tmp) " +
                " BEGIN " +
                " UPDATE Po_sign SET stage = stage - 1 WHERE uid = @uid AND rid = (SELECT TOP 1 rid FROM @tmp) " +
                " DELETE FROM @tmp WHERE rid = (SELECT TOP 1 rid FROM @tmp) " +
                " END " +
                " DELETE FROM Po_sign WHERE rid = @rid AND uid = @uid AND stage = @stage ");
            sqlCommand.Connection = sqlConnection;
            sqlCommand.Parameters.Add(new SqlParameter("@rid", rid));
            sqlCommand.Parameters.Add(new SqlParameter("@uid", uid));
            sqlCommand.Parameters.Add(new SqlParameter("@stage", stage));
            sqlCommand.ExecuteNonQuery();
            sqlConnection.Close();
        }