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sql語句from (select distinct Subject from tb) as什么意思

SQL Server

一只甜甜圈 2019-07-08 08:04:42

declare @sql varchar(8000)set @sql = 'select Name as ' + '姓名'select @sql = @sql + ' , max(case Subject when ''' + Subject + ''' then Result else 0 end) [' + Subject + ']'from (select distinct Subject from tb) as aset @sql = @sql + ' from tb group by name'exec(@sql)from (select distinct Subject from tb) as aas a必須要么。可不可以不要

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2 回答

UYOU

TA貢獻1878條經(jīng)驗獲得超4個贊

把子查詢：
select distinct Subject from tb
的結(jié)果作為一個表a來使用（理解成臨時視圖a也可以）

關(guān)于sql語句中 from 子表偽名的問題：

Oracle支持：
select * from (xxx)
select * from (xxx) a

SQL Server和db2支持：
select * from (xxx) as a
select * from (xxx) a

sybase 都不支持，另有寫法

所以，最好寫成：
select * from (xxx) a