SQL - 如何通過降序時間戳來查詢親子記錄

這裏是我的表SQL - 如何通過降序時間戳來查詢親子記錄

+------------+-----------+---------------+--------------+ 
| CommentId | ParentId | Timestamp | CommentText | 
+------------+---------+-----------+--------------------+ 
|   1 |  NULL | Jan 1 2:00pm |   a | 
|   2 |  NULL | Jan 1 2:01pm |   b | 
|   3 |   1 | Jan 1 3:03pm |   c | 
|   4 |   2 | Jan 1 5:00pm |   d | 
|   5 |   2 | Jan 1 5:01pm |   e | 
|   6 |  NULL | Jan 1 8:00pm |   f | 
|   7 |   1 | Jan 1 7:00pm |   g | 
|   8 |   6 | Jan 1 9:04pm |   h | 
|   9 |   1 | Jan 1 8:05pm |   i | 
|   10 |  NULL | Jan 1 9:04pm |   k | 
+------------+-----------+---------------+--------------+

目前我使用下面的SQL返回母公司下令評論

SELECT c.* 
FROM Comments c 
ORDER BY COALESCE(c.ParentId, c.Id)

結果是這樣的：

+------------+-----------+---------------+--------------+ 
| CommentId | ParentId | Timestamp | CommentText | 
+------------+---------+-----------+--------------------+ 
|   1 |  NULL | Jan 1 2:00pm |   a | 
|   3 |   1 | Jan 1 3:03pm |   c | 
|   7 |   1 | Jan 1 7:00pm |   g | 
|   9 |   1 | Jan 1 8:05pm |   i |  
|   2 |  NULL | Jan 1 2:01pm |   b |  
|   4 |   2 | Jan 1 5:00pm |   d | 
|   5 |   2 | Jan 1 5:01pm |   e | 
|   6 |  NULL | Jan 1 8:00pm |   f |  
|   8 |   6 | Jan 1 9:04pm |   h |  
|   10 |  NULL | Jan 1 9:04pm |   k | 
+------------+-----------+---------------+--------------+

我需要以降序時間戳順序得到結果。結果集應該是這樣的：

+------------+-----------+---------------+--------------+ 
| CommentId | ParentId | Timestamp | CommentText | 
+------------+---------+-----------+--------------------+   
|   10 |  NULL | Jan 1 9:04pm |   k | 
|   6 |  NULL | Jan 1 8:00pm |   f |  
|   8 |   6 | Jan 1 9:04pm |   h |  
|   2 |  NULL | Jan 1 2:01pm |   b |  
|   5 |   2 | Jan 1 5:01pm |   e | 
|   4 |   2 | Jan 1 5:00pm |   d | 
|   1 |  NULL | Jan 1 2:00pm |   a | 
|   9 |   1 | Jan 1 8:05pm |   i | 
|   7 |   1 | Jan 1 7:00pm |   g | 
|   3 |   1 | Jan 1 3:03pm |   c |  
+------------+-----------+---------------+--------------+

下不起作用：

SELECT c.* 
FROM Comments c 
ORDER BY COALESCE(c.ParentId, c.Id), Timestamp DESC

來源

2012-11-07 Bob

爲什麼你說它不起作用？我想你只是在你的訂單中缺少一個DESC – fthiella

是的，如果我添加沒有時間戳的DESC，它將大部分我想要的。它唯一不做的事情是以降序排列回覆（parentId！= NULL）。我意識到我沒有在我的問題中以降序排列答覆。我已經更新了它。 – Bob

我認爲這個查詢返回的順序行，你想：

SELECT c.* 
FROM Comments c 
ORDER BY 
    COALESCE(ParentID, ID) DESC, 
    ParentID is not null, 
    Timestamp DESC

它的訂單如果它不爲空，則由ParentID以降序排列，否則按ID排序，然後按空格排在頂部，然後按時間戳desc。

來源

2012-11-09 20:02:40 fthiella

我收到一個語法錯誤 - 關鍵字'IS'附近的語法不正確。 – Bob

你正在使用什麼DBMS？你可以嘗試用「ParentID不爲空」來描述這一行：'當ParentID爲NULL時，則爲0，否則爲1，' – fthiella

是的，這很有效！謝謝！ – Bob

SQL - 如何通過降序時間戳來查詢親子記錄

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