將子查詢中的1個字段與其他字段進行比較？

Question

我想比較兩個字段中的oracle select查詢作爲case語句的一部分，其中一個來自子查詢，但我得到錯誤。

E.g

select 1 as one, 
     (select 2 from dual) as two, 
     case when one=two then 'EQUAL' 
      else 'NOTEQUAL' 
     end match 
from dual; 

錯誤ORA-00904：雙無效標識符

思考如何改寫呢？

提前致謝！

Answer 1

問題是你不能使用別名在同一水平上，你需要做一個子查詢或CTE

WITH step1 as (
    select 1 as one 
    from dual 
), step2 as (
    select 2 as two 
    from dual 
) 
SELECT case when one=two then 'EQUAL' 
      else 'NOTEQUAL' 
     end match 
FROM step1 
CROSS JOIN step2 

Answer 2

你不能使用別名，所以你必須重寫數據源和子查詢。

SELECT 1 as one, 
     (SELECT 2 FROM dual) as two, 
     CASE WHEN 1 = (SELECT 2 FROM dual) 
      THEN 'EQUAL' 
      ELSE 'NOTEQUAL' 
     END match 
    FROM dual 

結果

one two match 
1 2 NOTEQUAL 

Answer 3

使用簡單的子查詢

Select t.*, 
     case when one=two then 'EQUAL' 
      else 'NOTEQUAL' 
     end match 
From (
    select 1 as one, 
      (select 2 from dual) as two 
    from dual 
) t;