从嵌套子查询联合中选择

Question

我很确定这是应用正确的别名的问题，我只是不确定我要出错的位置。本身

Select Z.DesiredResult1, etc... 
from (
    Select C.columns 
     from (
     Select B.columns 
      from (
       Select A.columns 
       from (Subquery) as A 
      ) as B 
     ) as C 
    Where C.condition = 1 
    UNION 
    Select F.columns 
     from (
     Select E.columns 
      from (
       Select D.columns 
       from (Subquery) as D 
      ) as E 
     ) as F 
    Where F.condition = 2 
) as Z 

工会功能完美，但努力使SELECT语句从它（如上图所示），当它抛出一个错误：我在SQLSERVER看着下面的UNION

No column name was specified for column 1 of 'Z'

任何见解，将不胜感激，感谢帮助SQL新手。

编辑：解决 - 我误解了错误。问题是一个聚合函数需要一个别名，而不是整个子查询。留下未命名的聚合列对单独工会来说工作得很好，所以我甚至没有考虑它。感谢您的阅读。

Answer 1

这个错误可以很容易地复制。检查它here。

如果你不命名单一UNION

SELECT * 
FROM (SELECT 'A','B') T1 
UNION 
SELECT * 
FROM (SELECT 'C','D') T2 

列，您将得到同样的错误：

No column name was specified for column 1 of 'T1'.

No column name was specified for column 2 of 'T1'.

No column name was specified for column 1 of 'T2'.

No column name was specified for column 2 of 'T2'.

简单的命名具有相同名称的每个公共列。

SELECT T3.Result1, T3.Result2 
FROM 
    (SELECT * 
    FROM (SELECT 'A' Result1, 'B' Result2) T1 
    UNION 
    SELECT * 
    FROM (SELECT 'C' Result1, 'D' Result2) T2) T3 

+----+---------+---------+ 
| | Result1 | Result2 | 
+----+---------+---------+ 
| 1 | A | B | 
+----+---------+---------+ 
| 2 | C | D | 
+----+---------+---------+