如斯的sql语句，求原理_Sql Server

如此的sql语句，求原理
select a.Estimated_Arrival_Date_s from (
select estimated_arrival_date Estimated_Arrival_Date_s from Is_Issues_Plan_Detail where Estimated_Arrival_Date_s='aa'
)a

如此的sql语句，求原理为什么不能用Estimated_Arrival_Date_s='aa' 只能用estimated_arrival_date=‘aa’，求原理。。。。。。。。。。。。。。。

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跟sql的执行顺序有关

SQL code

select a.Estimated_Arrival_Date_s from (select estimated_arrival_date Estimated_Arrival_Date_s from Is_Issues_Plan_Detail)awhere Estimated_Arrival_Date_s='aa'
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探讨

跟sql的执行顺序有关

SQL code
select a.Estimated_Arrival_Date_s from (
select estimated_arrival_date Estimated_Arrival_Date_s from Is_Issues_Plan_Detail)a
where Estimated_Arrival_Date_s='aa'

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UP一个。这地方都是sql高手，个人也标胶喜欢
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SQL codedeclare @T table (col varchar(1))insert into @Tselect 'a' union allselect 'b' union allselect 'c'--order by 后面就可以用别名select col a from @T order by a--where后面用别名的话就需要嵌套一层select col a from @T where a='b'/*Invalid column name 'a'.*/