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mysql - Sql union 操作

瀏覽:101日期:2022-06-14 10:08:09

問題描述

問題:第一種寫法:

(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

第二種寫法:

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’

為什么第二種寫法可以正確執(zhí)行,第一種方式就不可以??

區(qū)別 不是 第一種方式中給 臨時(shí)表起了個(gè)別名嘛,怎么就不行了?高人指點(diǎn)吶

問題解答

回答1:

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

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