Sql server SQL Server-运行嵌套查询需要40分钟

自2001年以来，我有一个非常大的web论坛应用程序，从SQLServer2012数据库运行，大约有2000万篇文章。数据文件的大小约为40GB

我在表中添加了相应字段的索引，但是此查询显示每个论坛中帖子的日期范围，运行大约需要40分钟：

SELECT
    T2.ForumId,
    Forums.Title,
    T2.ForumThreads,
    T2.ForumPosts,
    T2.ForumStart,
    T2.ForumStop

FROM
    Forums
    INNER JOIN (

    SELECT
        Min(ThreadStart) As ForumStart,
        Max(ThreadStop) As ForumStop,
        Count(*) As ForumThreads,
        Sum(ThreadPosts) As ForumPosts,
        Threads.ForumId
    FROM
        Threads
        INNER JOIN (

            SELECT
                Min(Posts.DateTime) As ThreadStart,
                Max(Posts.DateTime) As ThreadStop,
                Count(*) As ThreadPosts,
                Posts.ThreadId
            FROM
                Posts
            GROUP BY
                Posts.ThreadId

        ) As P2 ON Threads.ThreadId = P2.ThreadId

    GROUP BY
        Threads.ForumId

) AS T2 ON T2.ForumId = Forums.ForumId

我怎样才能加快速度呢

更新：

这是从右到左的估计执行计划：

[Path 1]

Clustered Index Scan (Clustered) [Posts].[PK_Posts], Cost: 98%
Hash Match (Partial Aggregate), Cost: 2%
Parallelism (Repartition Streams), Cost: 0%
Hash Match (Aggregate), Cost 0%
Compute Scalar, Cost: 0%
Bitmap (Bitmap Create), Cost: 0%

[Path 2]

Index Scan (NonClustered) [Threads].[IX_ForumId], Cost: 0%
Parallelism (Repartition Streams), Cost: 0%

[Path 1 and 2 converge into Path 3]

Hash Match (Inner Join), Cost: 0%
Hash Match (Partial Agregate), Cost: 0%
Parallelism (Repartition Streams), Cost: 0%
Sort, Cost: 0%
Stream Aggregate (Aggregate), Cost: 0%
Compute Scalar, Cost: 0%

[Path 4]
Clustered Index Seek (Clustered) [Forums].[PK_Forums], Cost: 0%

[Path 3 and 4 converge into Path 5]

Nested Loops (Inner Join), Cost: 0%
Paralleism (Gather Streams), Cost: 0%
SELECT, Cost: 0%

---

您是否尝试过将这两个派生表放入临时表中？SQL Server将从它们的单个列中获取统计信息，您也可以在它们上放置索引

---

此外，乍一看，索引视图在这里可能会有所帮助，因为您有很多聚合。

您是否尝试过将这两个派生表放入临时表中？SQL Server将从它们的单个列中获取统计信息，您也可以在它们上放置索引

---

此外，乍一看索引视图在这里可能会有所帮助，因为您有很多聚合。

您真的需要聚合两次吗？这个查询会给你同样的结果吗

SELECT 
T2.ForumId, 
Forums.Title, 
T2.ForumThreads, 
T2.ForumPosts, 
T2.ForumStart, 
T2.ForumStop  
FROM 
    Forums 
INNER JOIN (  
    SELECT
         Min(ThreadStart) As ForumStart,
         Max(ThreadStop) As ForumStop,     
         Count(*) As ForumThreads,     
         Sum(ThreadPosts) As ForumPosts,     
         Threads.ForumId 
    FROM     
        Threads     
    INNER JOIN (          
                SELECT             
                    Posts.DateTime As ThreadStart,             
                    Posts.DateTime As ThreadStop,             
                    Count(*) As ThreadPosts,             
                    Posts.ThreadId         
                FROM             
                    Posts         
                 ) As P2 ON Threads.ThreadId = P2.ThreadId  
    GROUP BY     
        Threads.ForumId  
    ) AS T2 ON T2.ForumId = Forums.ForumId 

---

你真的需要聚合两次吗？这个查询会给你同样的结果吗

SELECT 
T2.ForumId, 
Forums.Title, 
T2.ForumThreads, 
T2.ForumPosts, 
T2.ForumStart, 
T2.ForumStop  
FROM 
    Forums 
INNER JOIN (  
    SELECT
         Min(ThreadStart) As ForumStart,
         Max(ThreadStop) As ForumStop,     
         Count(*) As ForumThreads,     
         Sum(ThreadPosts) As ForumPosts,     
         Threads.ForumId 
    FROM     
        Threads     
    INNER JOIN (          
                SELECT             
                    Posts.DateTime As ThreadStart,             
                    Posts.DateTime As ThreadStop,             
                    Count(*) As ThreadPosts,             
                    Posts.ThreadId         
                FROM             
                    Posts         
                 ) As P2 ON Threads.ThreadId = P2.ThreadId  
    GROUP BY     
        Threads.ForumId  
    ) AS T2 ON T2.ForumId = Forums.ForumId 

---

像这样的怎么样？不管怎样，你明白了

SELECT f.ForumID,
f.Title,
MIN(p.[DateTime]) as ForumStart,
MAX(p.[DateTime]) as ForumStop,
COUNT(DISTINCT f.ForumID) as ForumPosts,
COUNT(DISTINCT t.ThreadID) as ForumThreads
FROM Forums f
INNER JOIN Threads t
ON f.ForumID = t.ForumID
INNER JOIN Posts p
ON p.ThreadID = p.ThreadID
GROUP BY f.ForumID, f.Title

---

像这样的怎么样？不管怎样，你明白了

SELECT f.ForumID,
f.Title,
MIN(p.[DateTime]) as ForumStart,
MAX(p.[DateTime]) as ForumStop,
COUNT(DISTINCT f.ForumID) as ForumPosts,
COUNT(DISTINCT t.ThreadID) as ForumThreads
FROM Forums f
INNER JOIN Threads t
ON f.ForumID = t.ForumID
INNER JOIN Posts p
ON p.ThreadID = p.ThreadID
GROUP BY f.ForumID, f.Title

---

当您确实从中选择时，索引可能会起作用，但子查询的结果不会被索引。加入它们可能会扼杀性能

正如buckley所建议的，我会尝试将中间结果存储在临时表中，并在执行最终查询之前添加索引

---

但是外部选择不包括特定于线程的信息。看起来查询只是按论坛选择最小/最大日期。如果是这样的话，您只需按论坛分组获得min/max/count帖子。

当您选择FROM时，索引可能会起作用，但子查询的结果不会被索引。加入它们可能会扼杀性能

正如buckley所建议的，我会尝试将中间结果存储在临时表中，并在执行最终查询之前添加索引

---

但是外部选择不包括特定于线程的信息。看起来查询只是按论坛选择最小/最大日期。如果是这样的话，你只需要得到按论坛分组的min/max/count帖子。

如果你通过向posts表中添加ForumId来取消规范化，你就可以直接从posts表中查询所有的统计信息。有了正确的索引，这可能会表现得很好。当然，在插入Posts表时，这需要对代码进行一点小的更改，以包括ForumId…

如果通过将ForumId添加到Posts表来取消规范化，则可以直接从Posts表中查询所有统计信息。有了正确的索引，这可能会表现得很好。当然，在插入Posts表时，这需要对代码进行一点小的修改，以包含ForumId…

我向数据库添加了更多索引，这大大加快了速度。执行时间现在大约是20秒！！。我承认，添加的许多索引都是猜测或随机添加的。

我向数据库添加了更多索引，这大大加快了速度。执行时间现在大约是20秒！！。我承认，添加的许多索引都是猜测或随机添加的。

查询的执行计划是什么样子的？40Gig？不足为奇。。添加索引！通过添加、更改索引，使这些扫描成为搜索，它会变得更好。您可能希望将表拆分为分区。查询的执行计划是什么样子的？40Gig？不足为奇。。添加索引！通过添加、更改索引，使这些扫描成为搜索，它会变得更好。您可能希望将表拆分为分区。+1，当我看到您的几乎相同的解决方案时，我已经发布并删除了。但是，f.forumid不应该是*？这是每个ForumID的帖子数量+1，当我看到你的几乎相同的解决方案时，我已经发布并删除了。但是，f.forumid不应该是*？它是每个ForumID的帖子数。