mysql - Sql union 操作
問(wèn)題描述
問(wèn)題：第一種寫(xiě)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(xiě)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(xiě)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(wèn)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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