http://www.newxing.com/Tech/Database/MSSQL/91.html------------------同意

http://hi.baidu.com/hellofrancis/item/1db89f0a2673f1036d904805-----這個說法好像不對

別名的有效性也是遵循sql執行順序的，你不能在執行別名命名語句之前就使用它。

例如下面的SQL語句: 

select id, (c1 + c2) as s
from t1
where s > 100 

select id, (c1 + c2) as
 
 s
from t1
where (c1 + c2) > 100 

 就沒問題了.

select t2.*
from (select id, (c1 + c2) as c from t1) t2
where c > 100
 
  --或者
 
select t2.*
from (select id, c = c1+c2 from t1) t2
where c > 100