三张表,联表查询,这个sql还能再优化吗
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2022-06-05 10:20:54
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SELECT c.username,c.sex,c.attentions,c.fans,a.
FROM (wb_userinfo c LEFT JOIN wb_weibo a ON c.uid = a.uid)
LEFT JOIN wb_picture b ON 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;
回复内容:
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;
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;
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。
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
不要用join