mysql - Sql union 操作

问题描述

问题：第一种写法：

(select du.day,du.apptoken ,du.version, du.channel,du.city,du.count,concat(apptoken, version,channel,city) as joinkey from day_new_users_count du where day=’20170319’) as dayUsers union (select tu.day,tu.apptoken,tu.version,tu.channel,tu.city,tu.count,concat(apptoken,version,channel,city) as joinkey from total_users tu where day=’20170318’) as toUsers

第二种写法：

select du.day,du.apptoken ,du.version, du.channel,du.city,du.count,concat(apptoken, version,channel,city) as joinkey from day_new_users_count du where day=’20170319’ union select tu.day,tu.apptoken,tu.version,tu.channel,tu.city,tu.count,concat(apptoken,version,channel,city) as joinkey from total_users tu where day=’20170318’

为什么第二种写法可以正确执行，第一种方式就不可以？？

区别 不是 第一种方式中给 临时表起了个别名嘛，怎么就不行了？高人指点呐

问题解答

select * from (selectdu.day, du.apptoken , du.version, du.channel, du.city, du.count,concat(apptoken, version,channel,city) as joinkeyfrom day_new_users_count duwhere day=’20170319’) as dayUsersunionselect * from (selecttu.day, tu.apptoken, tu.version, tu.channel, tu.city, tu.count,concat(apptoken,version,channel,city) as joinkeyfrom total_users tuwhere day=’20170318’) as toUsers