mysql union order by 子查询排序不生效

时间 2019-12-23

标签 mysql union order 查询排序生效栏目 MySQL 繁體版

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其实这么写理论上是对的，不少博客教程都是这样子写的。。优化

select * from (SELECT * FROM article WHERE is_top=0 ORDER BY id DESC) as t1排序

union教程

select * from (SELECT * FROM article WHERE is_top=1 ORDER BY start_time desc) as t2博客

而后仍是发现子查询的排序无效，尴尬，后来才发现若是order by 不带limit，会被优化器干掉，致使语句就是：it

select * from (SELECT * FROM article WHERE is_top=0 ) as t1io

unionselect

select * from (SELECT * FROM article WHERE is_top=1) as t2nio

解决方案：im

select * from (SELECT * FROM article WHERE is_top=0 ORDER BY id DESC limit 999999) as t1查询

union

select * from (SELECT * FROM article WHERE is_top=1 ORDER BY start_time desc limit 999999) as t2