Question

我正在使用以下查询来执行此操作

select (Col_A + Col_B) Foo,
       (Col_C + Col_D) Bar,
       (Col_A + Col_B + Col_C + Col_D) FooBar from Table1

但有没有像这样做的方式

select (Col_A + Col_B) Foo,
       (Col_C + Col_D) Bar,
       (Foo + Bar) FooBar from Table1

它给出错误

'Invalid Column Foo'
'Invalid Column Bar'

如何解决这个问题？

Answer 1

部分解决方案是使用with构造：

with query as (
  select (Col_A + Col_B) Foo,
         (Col_C + Col_D) Bar
    from Table1)

select Foo,
       Bar,
       Foo + Bar
  from query

Answer 2

Afaik那些你所指的那些专栏尚未被这些名称存在。

您当然可以尝试以下方式：

SELECT *, (Foo + Bar) FooBar
FROM (select (Col_A + Col_B) Foo,
       (Col_C + Col_D) Bar
     from Table1) SRC

Answer 3

SQL在SELECT之前解析FROM，因此您需要在FROM子句中添加别名

SELECT Foo
      ,Bar
      ,Foo + Bar
FROM Table1
     CROSS APPLY (
         SELECT Col_A + Col_B AS Foo
               ,Col_C + Col_D AS Bar
     ) AS CA1

如何在SQL中添加动态列？

3 个答案: