MySQL Select查询执行缓慢

Question

我有以下查询...

SELECT DISTINCT * FROM 
vPAS_Posts_Users 
WHERE (post_user_id =:id AND post_type != 4) 
AND post_updated >:updated 
GROUP BY post_post_id 
UNION 
SELECT DISTINCT vPAS_Posts_Users.* FROM PAS_Follow 
JOIN vPAS_Posts_Users ON 
( PAS_Follow.folw_followed_user_id = vPAS_Posts_Users.post_user_id ) 
WHERE (( PAS_Follow.folw_follower_user_id =:id AND PAS_Follow.folw_deleted = 0 ) 
OR ( post_type = 4 AND post_passed_on_by = PAS_Follow.folw_follower_user_id 
AND post_user_id !=:id )) 
AND post_updated >:updated 
GROUP BY post_post_id ORDER BY post_posted_date DESC LIMIT :limit

例如:id = 7 ， :updated = 0.0和:limit=40

我的问题是查询需要大约一分钟才能返回结果。 此查询中有什么我可以做以加快结果的速度吗？

我正在使用RDS

********编辑*********

我被要求使用EXPLAIN运行查询，结果如下

******** EDIT **********查看定义

CREATE ALGORITHM=UNDEFINED DEFINER=`MySQLUSer`@`%` SQL SECURITY DEFINER VIEW `vPAS_Posts_Users`
AS SELECT
   `PAS_User`.`user_user_id` AS `user_user_id`,
   `PAS_User`.`user_country` AS `user_country`,
   `PAS_User`.`user_city` AS `user_city`,
   `PAS_User`.`user_company` AS `user_company`,
   `PAS_User`.`user_account_type` AS `user_account_type`,
   `PAS_User`.`user_account_premium` AS `user_account_premium`,
   `PAS_User`.`user_sign_up_date` AS `user_sign_up_date`,
   `PAS_User`.`user_first_name` AS `user_first_name`,
   `PAS_User`.`user_last_name` AS `user_last_name`,
   `PAS_User`.`user_avatar_url` AS `user_avatar_url`,
   `PAS_User`.`user_cover_image_url` AS `user_cover_image_url`,
   `PAS_User`.`user_bio` AS `user_bio`,
   `PAS_User`.`user_telephone` AS `user_telephone`,
   `PAS_User`.`user_dob` AS `user_dob`,
   `PAS_User`.`user_sector` AS `user_sector`,
   `PAS_User`.`user_job_type` AS `user_job_type`,
   `PAS_User`.`user_unique` AS `user_unique`,
   `PAS_User`.`user_deleted` AS `user_deleted`,
   `PAS_User`.`user_updated` AS `user_updated`,
   `PAS_Post`.`post_post_id` AS `post_post_id`,
   `PAS_Post`.`post_language_id` AS `post_language_id`,
   `PAS_Post`.`post_type` AS `post_type`,
   `PAS_Post`.`post_promoted` AS `post_promoted`,
   `PAS_Post`.`post_user_id` AS `post_user_id`,
   `PAS_Post`.`post_posted_date` AS `post_posted_date`,
   `PAS_Post`.`post_latitude` AS `post_latitude`,
   `PAS_Post`.`post_longitude` AS `post_longitude`,
   `PAS_Post`.`post_location_name` AS `post_location_name`,
   `PAS_Post`.`post_text` AS `post_text`,
   `PAS_Post`.`post_media_url` AS `post_media_url`,
   `PAS_Post`.`post_image_height` AS `post_image_height`,
   `PAS_Post`.`post_link` AS `post_link`,
   `PAS_Post`.`post_link_title` AS `post_link_title`,
   `PAS_Post`.`post_unique` AS `post_unique`,
   `PAS_Post`.`post_deleted` AS `post_deleted`,
   `PAS_Post`.`post_updated` AS `post_updated`,
   `PAS_Post`.`post_original_post_id` AS `post_original_post_id`,
   `PAS_Post`.`post_original_type` AS `post_original_type`,
   `PAS_Post`.`post_passed_on_by` AS `post_passed_on_by`,
   `PAS_Post`.`post_passed_on_caption` AS `post_passed_on_caption`,
   `PAS_Post`.`post_passed_on_fullname` AS `post_passed_on_fullname`,
   `PAS_Post`.`post_passed_on_avatar_url` AS `post_passed_on_avatar_url`
FROM (`PAS_User` join `PAS_Post` on((`PAS_User`.`user_user_id` = `PAS_Post`.`post_user_id`)));

Answer 1

试试这个查询：

SELECT * 
FROM 
    vPAS_Posts_Users 
WHERE 
    post_user_id =:id 
AND post_type != 4 
AND post_updated > :updated 
UNION 
SELECT u.* 
FROM vPAS_Posts_Users u
        JOIN PAS_Follow f ON f.folw_followed_user_id = u.post_user_id
WHERE 
    u.post_updated > :updated
AND (   (f.folw_follower_user_id = :id AND f.folw_deleted = 0) 
    OR  (u.post_type = 4 AND u.post_passed_on_by = f.folw_follower_user_id AND u.post_user_id != :id)
) 
ORDER BY u.post_posted_date DESC;
LIMIT :limit

---

其他改进

索引：确保在以下列上有索引：

• PAS_User.user_user_id
• PAS_Post.post_user_id
• PAS_Post.post_type
• PAS_Post.post_updated
• PAS_Follow.folw_followed_user_id
• PAS_Follow.folw_deleted
• PAS_Post.post_passed_on_by

完成之后，请1-再次检查性能（SQL_NO_CACHE），然后2提取另一个说明计划，以便我们可以调整查询。

---

说明结果

Answer 2

以下是有关查询的一些建议，并首先对两个结果集使用UNION进行查看，这可能会使查询工作缓慢，而可以使用UNION ALL

为什么我要让您使用UNION ALL

原因是UNION ALL和UNION使用临时表来生成结果。执行速度的差异是因为UNION要求内部临时表带有索引（以跳过重复的行），而UNION ALL将创建不具有此类索引的表。使用UNION ALL时的性能改进。 UNION会自行删除所有重复的记录，因此无需使用DISTINCT子句，仅尝试按子查询查询整个结果集中的一个GROUP BY，这也将最小化执行时间，而不是对每个子查询进行结果分组。

确保在列上添加了正确的索引，尤其是在WHERE,ORDER BY, GROUP BY中使用的列，相对于其中的数据性质，数据类型应该适合于每个列，例如post_posted_date应该是datetime，date与索引也。

这是查询的基本思路

SELECT q.* FROM (
SELECT * FROM 
vPAS_Posts_Users 
WHERE (post_user_id =:id AND post_type != 4) 
AND post_updated >:updated 

UNION ALL


SELECT vPAS_Posts_Users.* FROM PAS_Follow 
JOIN vPAS_Posts_Users ON 
( PAS_Follow.folw_followed_user_id = vPAS_Posts_Users.post_user_id 
AND vPAS_Posts_Users.post_updated >:updated) 
WHERE (( PAS_Follow.folw_follower_user_id =:id AND PAS_Follow.folw_deleted = 0 ) 
OR ( post_type = 4 AND post_passed_on_by = PAS_Follow.folw_follower_user_id 
AND post_user_id !=:id )) 

) q
GROUP BY q.post_post_id ORDER BY q.post_posted_date DESC LIMIT :limit

参考

Union与Union All之间的差异–最佳性能比较

优化Mysql联合

MySQL性能博客

Answer 3

从您的解释中，我可以看到您的大多数表除了主键外没有其他键，我建议您在要连接的列上添加一些额外的键，例如：PAS_Follow.folw_followed_user_id和vPAS_Posts_Users.post_user_id，仅此将大大提高性能。

再见Gnagno