云蹦迪源码下载记⼀次MySQL多表联查时多个leftjoin优化从以前的30s左右到优化后的0.07s，速度嗖嗖的，原sql及具体优化如下：
mysql面试题sql语句多表联查--⽅法⼀：
SELECT s.id ,s.title
FROM school s
LEFT JOIN area_school_link asl ON s.id = asl.school_id
execution riskLEFT JOIN sys_area t1 ON asl.area_id = t1.id
LEFT JOIN sys_area t2 ON t1.parent_id = t2.id
WHERE s.deleted =0 and (t2.id =27 or t1.id =27)
--原先代码执⾏31s
饿了吗ui
SELECT s.id ,s.title
FROM school s INNER JOIN (SELECT a.area_id,a.school_id FROM area_school_link a) b ON s.id = b.school_id        LEFT JOIN sys_area t1 ON b.area_id = t1.id
LEFT JOIN sys_area t2 ON t1.parent_id = t2.id
winform textview 边框WHERE s.deleted =0 and (t2.id =27 or t1.id =27)
--优化后代码执⾏0.07s
--⽅法⼆：
--创建索引
create unique index index_id on school(id);
--删除索引
drop index index_id on school;
>inline在c语言中是什么意思

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