php - 三张表，联表查询，这个sql还能再优化吗

Question

SELECT c.username,c.sex,c.attentions,c.fans,a.id,a.content,a.isnum,a.times,a.turm,a.keep,a.comments,a.uid,b.mini,b.mednum,b.maxs
FROM (wb_userinfo c LEFT JOIN wb_weibo a ON c.uid = a.uid)
LEFT JOIN wb_picture b ON a.id = b.wid WHERE a.uid IN(SELECT follow FROM wb_follow WHERE fans = 27) OR a.uid = 27 ORDER BY a.times LIMIT 0,10;

Answer 1

有用or的可以考虑换成用union来尝试下

(SELECT c.username,c.sex,c.attentions,c.fans,a.id,a.content,a.isnum,a.times,a.turm,a.keep,a.comments,a.uid,b.mini,b.mednum,b.maxs
FROM (wb_userinfo c LEFT JOIN wb_weibo a ON c.uid = a.uid)
LEFT JOIN wb_picture b ON a.id = b.wid WHERE a.uid IN(SELECT follow FROM wb_follow WHERE fans = 27) )
union
(SELECT c.username,c.sex,c.attentions,c.fans,a.id,a.content,a.isnum,a.times,a.turm,a.keep,a.comments,a.uid,b.mini,b.mednum,b.maxs
FROM (wb_userinfo c LEFT JOIN wb_weibo a ON c.uid = a.uid)
LEFT JOIN wb_picture b ON a.id = b.wid WHERE a.uid = 27 )
ORDER BY a.times LIMIT 0,10;

Answer 2

使用explain看看分析报告贴出来看下，ref的值与row是的值索引使用情况等，连表查询的话我正常建议是拆成简单查询来。

Answer 3

就sql而言，可优化的空间不大，建议拆成若干条简单的sql，在代码里实现最终业务逻辑。

PS：尽量避免在sql里出现or

Answer 4

不要用join