mysql语句请尽量不使用ORDER BY RAND()

不使用ORDER BY RAND()

select id from `dynamic` order by rand() limit 1000;

上面的SQL语句，可优化为：

select id from `dynamic` t1 join (select rand() * (select max(id) from `dynamic`) as nid) t2 on t1.id > t2.nidlimit 1000;


区分in和exists、not in和not exists

原SQL语句：

select * from 表A where exists(select * from 表B where 表B.id=表A.id)

高效的SQL语句：

select colname … from A表 Left join B表 on where a.id = b.id where b.id is null