the query running too slow

Question

Given is mySQL table named "user_posts" with the following relevant fields:

• user_id
• user_status
• influencer_status

indexed in all three fields

My running slow query is here and also i have created an dbFiddle . Output of Explain is in the dbfiddle:

SELECT 
   P.user_post_id,     
   P.user_id_fk,P.post_type,
   P.who_can_see_post,
   P.post_image_id,P.post_video_id, 
   U.user_name, U.user_fullname,U.influencer_status 
 FROM user_posts P FORCE INDEX (ix_user_posts_post_id_post_type)
   INNER JOIN users U FORCE INDEX (ix_status_istatus)
   ON P.user_id_fk = U.user_id 
 WHERE 
   U.user_status='1' AND 
   U.influencer_status = '1' AND 
   (P.who_can_see_post IN('everyone','influencer','friends')) AND 
   (P.post_type IN('image','video'))
   AND p.user_post_id > 30
 ORDER BY 
    P.user_post_id 
 DESC LIMIT 30

The query takes extremely long, around 6-15 seconds. The database is not very busy otherwise and performs well on other queries.

I am obviously wondering why the query is so slow.

Is there a way to tell exactly what is taking mySQL so long? Or is there any change I need to make to make the query run faster?

Answer 1

ix_status_istatus密钥的定义阻止了它用于优化WHERE子句，因为它包括了user_id未在WHERE子句中使用的密钥。将索引重新定义为

ALTER TABLE `users`
  ADD PRIMARY KEY (`user_id`),
  ADD KEY ix_status_istatus (user_status, influencer_status);

允许其使用，并应加快您的查询，改变对搜索users使用index代替temporary and filesort。

dbfiddle上的演示

更新资料

对dbfiddle的进一步分析表明，最好将它FORCE INDEX从P表中删除，因为它是不必要的（仅PRIMARY需要键），并将其更改JOIN为a，STRAIGHT_JOIN即写为JOINas：

FROM user_posts P 
STRAIGHT_JOIN users U FORCE INDEX (ix_status_istatus)
ON P.user_id_fk = U.user_id