Mysql查询，使用ORDER BY时运行缓慢

Question

使用 ORDER BY 子句时，我的查询运行缓慢。

具有最大行数的表，包括大约。 30.000 行。

结果是 10 行，大约需要 0.2 秒。

如果没有“ORDER BY id DESC”，则需要 0.01 秒。

我查看了堆栈上的其他帖子并尝试优化此脚本，但我的知识已达到极限。

我还为所有列连接、WHERE、ORDER by 创建了索引。

您有什么可以改进的地方，或者关于如何通过返回更快的结果来下订单的想法？

Mysql 是这样的

SELECT  *
    FROM  
        ( SELECT  posts.id, posts.createdDateTime, posts.caption, posts.postUrl,
                posts.isVideo, posts.paymentType, posts.postPrice, profile.name,
                profile.username, 
                ( SELECT  COUNT(*)
                    FROM  likes
                    where  likes.postIdFK=posts.id
                ) as likes, 
                ( SELECT  COUNT(*)
                    FROM  likes
                    where  likes.postIdFK=posts.id
                      AND  likes.userIdFK=21643
                ) as myLike, 
                ( SELECT  COUNT(*)
                    FROM  comments
                    where  comments.postIdFK=posts.id
                      AND  comments.deleted=0
                ) as comments
            FROM  posts
            JOIN  users AS profile  ON posts.userIdFK=profile.id
            WHERE  posts.deleted=0
              AND  profile.deleted=0
              AND  ( posts.userIdFK IN (
                        SELECT  subscribedToProfileIdFK
                            FROM  
                                ( SELECT  userSubscriptions.subscribedToProfileIdFK, max(monthlySubscriptions.endSubscription) endSubscription
                                    FROM  userSubscriptions
                                    LEFT JOIN  monthlySubscriptions  ON monthlySubscriptions.userSubscriptionId=userSubscriptions.id
                                    WHERE  userSubscriptions.userIdFK=21643
                                      AND  userSubscriptions.quickpayComplete=1
                                    GROUP BY  userSubscriptions.id 
                          ) t
                            WHERE  (t.endSubscription >= CURDATE())
                            GROUP BY  t.subscribedToProfileIdFK )
                      OR  posts.id IN (
                        SELECT  paidPosts.postIdFK
                            FROM  paidPosts
                            WHERE  paidPosts.userIdFK=21643 
                          )
                      OR  posts.userIDFK=21643 ) 
        ) AS row
    ORDER BY  id DESC
    LIMIT  0,10

解释看起来像这样

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	profile	ref	PRIMARY,deleted	deleted	1	const	5410	Using temporary; Using filesort
1	PRIMARY	posts	ref	userIdFK,deleted	userIdFK	4	admin_slc.profile.id	1	Using where
8	MATERIALIZED	paidPosts	ALL	userIdFK,postIdFK	NULL	NULL	NULL	5	Using where
6	MATERIALIZED		ALL	NULL	NULL	NULL	NULL	14	Using where
7	DERIVED	userSubscriptions	index	userIdFK, quickpayComplete	PRIMARY	4	NULL	15	Using where
7	DERIVED	monthlySubscriptions	ref	userSubscriptionId	userSubscriptionId	4	admin_slc.userSubscriptions.id	1
5	DEPENDENT SUBQUERY	comments	ref	postIdFK,deleted	postIdFK	4	admin_slc.posts.id	1	Using where
4	DEPENDENT SUBQUERY	likes	ref	userIdFK,postIdFK	postIdFK	4	admin_slc.posts.id	1	Using where
3	DEPENDENT SUBQUERY	likes	ref	postIdFK	postIdFK	4	admin_slc.posts.id	1	Using index

如果您需要表定义，请告诉我。

//谢谢

Answer 1

您绝对可以重写此查询以从 SELECT 子句中删除选择查询，如下所示：

SELECT * FROM ( 
    SELECT posts.id, 
           posts.createdDateTime,  
           posts.caption,  
           posts.postUrl,  
           posts.isVideo,  
           posts.paymentType,  
           posts.postPrice, 
           profile.name,  
           profile.username,
           l.cnt as likes,
           ml.cnt as myLike,
           comm.cnt as comments -- as comments
    FROM posts 
    JOIN users AS profile ON posts.userIdFK=profile.id
    LEFT JOIN (SELECT likes.postIdFK, COUNT(*) as cnt FROM likes group by likes.postIdFK) as l 
      on l.postIdFK=posts.id
    LEFT JOIN (SELECT likes.postIdFK, COUNT(*) as cnt FROM likes where likes.userIdFK=21643 group by likes.postIdFK) ml 
      on ml.postIdFK=posts.id
    LEFT JOIN (SELECT comments.postIdFK, COUNT(*) as cnt FROM comments where comments.deleted=0 group by comments.postIdFK) as comm 
       on comm.postIdFK=posts.id
    WHERE posts.deleted=0 
    AND profile.deleted=0
    AND ( posts.userIdFK IN (
            SELECT subscribedToProfileIdFK 
              FROM (SELECT userSubscriptions.subscribedToProfileIdFK,
                           max(monthlySubscriptions.endSubscription) endSubscription
                      FROM userSubscriptions 
                      LEFT JOIN monthlySubscriptions ON monthlySubscriptions.userSubscriptionId=userSubscriptions.id 
                     WHERE userSubscriptions.userIdFK=21643 
                       AND userSubscriptions.quickpayComplete=1
                     GROUP BY userSubscriptions.id) t
            WHERE (t.endSubscription >= CURDATE())
           -- GROUP BY t.subscribedToProfileIdFK -- this group by is not needed
           )
        OR exists 
           (SELECT 1 
              FROM paidPosts 
             WHERE paidPosts.userIdFK=21643
               AND posts.id = paidPosts.postIdFK)
        OR posts.userIDFK=21643 
     )
) AS row
ORDER BY id DESC
LIMIT 0,10