SQL Server 2008線程評論系統 - 什麼更有效？

Question

我有一張表，其中包含我的帖子和我的意見。我們只發表一條評論，對評論沒有評論。現在，我們正在對帖子進行ajax請求，然後在另一個查詢中抓取註釋，使用父帖子ID來獲取適當的子註釋。

我想要做的就是將其整合到最高效的單一查詢系統中。

這讓我要麼使用CROSS APPLY，或UNION，如果我沒有記錯，但也有一些注意事項：

• 我們要選擇的十大職位，頂部2每個
• 帖子評論需要按降序列出
• 評論需要按升序排列

這裏上市是我們的CUR的例子租查詢的文章和評論：

帖子：

SELECT TOP 10 ForumPostID, ForumID, ContentText, Hidden, S.Firstname, S.Lastname, 
CONVERT(VARCHAR(30),DATEADD(hh,CASE 
     WHEN DD.StartDate IS NOT NULL THEN 5 ELSE 6 
     END, 
FP.PostDate),126)+'Z' AS PostDate, 
PostDate AS UglyTime, TopPostID, 
(SELECT COUNT(*) FROM Admin.dbo.ForumPosts WHERE TopPostID = FP.ForumPostID) AS  
'CommentCount', 
(SELECT COUNT(*) FROM Admin.dbo.ForumLikes WHERE ForumPostID = FP.ForumPostID) AS 'Likes',  
CASE (SELECT COUNT(*) FROM Admin.dbo.ForumLikes WHERE ForumPostID = FP.ForumPostID AND  
     Authuser = FP.Authuser) WHEN 0 THEN 'Like' ELSE 'You liked this.' END AS 'LikeText' 
FROM Admin.dbo.ForumPosts FP 
INNER JOIN Student.dbo.Student S 
     ON S.StudentUID = FP.Authuser 
INNER JOIN Admin.dbo.DayLightSavingsDates DD 
     ON FP.PostDate BETWEEN DD.StartDate AND DD.EndDate 
WHERE FP.ForumPostID NOT IN (SELECT Top 0 ForumPostID FROM Admin.dbo.ForumPosts FP2 ORDER BY 
FP2.ForumPostID DESC) 
AND FP.Hidden = 'N' AND FP.ContentText <> '' 
AND FP.PostType = 'post' 
ORDER BY FP.PostDate DESC 

評論：

SELECT TOP 50 ForumPostID, ForumID, ContentText, Hidden, S.Firstname, S.Lastname, 
CONVERT(VARCHAR(30),DATEADD(hh,CASE 
     WHEN DD.StartDate IS NOT NULL THEN 5 ELSE 6 END, 
FP.PostDate),126)+'Z' AS PostDate, 
PostDate AS UglyTime, TopPostID, 
(SELECT COUNT(*) FROM Admin.dbo.ForumPosts WHERE TopPostID = FP.ForumPostID) AS  
     'CommentCount', 
(SELECT COUNT(*) FROM Admin.dbo.ForumLikes WHERE ForumPostID = FP.ForumPostID) AS 'Likes', 
CASE (SELECT COUNT(*) FROM Admin.dbo.ForumLikes WHERE ForumPostID = FP.ForumPostID AND 
    Authuser = FP.Authuser) WHEN 0 THEN 'Like' ELSE 'You liked this.' END AS 'LikeText' 
FROM Admin.dbo.ForumPosts FP 
INNER JOIN Student .dbo.Student S 
ON S.StudentUID = FP.Authuser 
INNER JOIN Admin.dbo.DayLightSavingsDates DD ON FP.PostDate BETWEEN DD.StartDate AND DD.EndDate 
WHERE FP.ForumPostID NOT IN 
    (SELECT Top 0 ForumPostID FROM Admin.dbo.ForumPosts FP2 ORDER BY FP2.ForumPostID DESC) 
AND FP.ForumPostID IN 
    (SELECT Top 2 ForumPostID FROM Admin.dbo.ForumPosts FP3 WHERE FP3.TopPostID = FP.TopPostID 
     ORDER BY FP3.PostDate DESC) 
AND FP.Hidden = 'N' 
AND FP.ContentText <> '' 
AND FP.PostType = 'comment' 
AND FP.TopPostID IN (373, 371, 370, 369, 368, 367, 366, 365, 364, 363) 
ORDER BY FP.ForumPostID ASC 

Answer 1

，可以在這裏給出的是你需要看的執行計劃中最重要的建議。我不知道這個方法。查詢太複雜，無法提供具體建議。

但有一件事：你有很多表達式「（SELECT COUNT（*）FROM Admin.dbo.ForumPosts WHERE TopPostID = FP.ForumPostID）」。 SQL Server查詢優化器在計算中使用這些表達式時遇到問題。它有時無法將它們轉換爲正常的連接，從而阻礙了很多優化。你可能想把它們轉換成連接。儘管我現在可以說IN子句是安全的。