原來，union的優(yōu)先級很高。比如

select stdname,[subject]='化學(xué)',化學(xué) as score from #student2 union all select stdname,[subject]='數(shù)學(xué)',數(shù)學(xué) as score from #student2 union all select stdname,[subject]='物理',物理 as score from #student2 union all select stdname,[subject]='語文',語文 as score from #student2 order by stdname,[subject]
等同于

select * from( select stdname,[subject]='化學(xué)',化學(xué) as score from #student2 union all select stdname,[subject]='數(shù)學(xué)',數(shù)學(xué) as score from #student2 union all select stdname,[subject]='物理',物理 as score from #student2 union all select stdname,[subject]='語文',語文 as score from #student2 ) as a order by stdname,[subject]

轉(zhuǎn)載于:https://www.cnblogs.com/leftfist/archive/2013/06/15/4258014.html

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