行的計算後創建一個別名？

Question

有一種方法可以在計算後創建一個別名？

在實踐中有寫這個更好的方法：

select 
    case when aaa ... then then else end AS ALIAS1, 
    case when bbb ... then then else end AS ALIAS2, 
    case when ccc ... then then else end AS ALIAS3, 
    /* the sum of previous aliases */ 
    case when aaa ... then then else end + 
    case when bbb ... then then else end + 
    case when ccc ... then then else end AS ALIAS_SUM 

預先感謝您

Answer 1

你可以做這樣的事情。這樣你就不會兩次處理這些案件。

SELECT *, ALIAS1 + ALIAS2 + ALIAS3 AS ALIAS_SUM 
FROM 
(
    SELECT 
     CASE WHEN aaa ... THEN ... ELSE END AS ALIAS1, 
     CASE WHEN bbb ... THEN ... ELSE END AS ALIAS2, 
     CASE WHEN ccc ... THEN ... ELSE END AS ALIAS3 
    FROM... 
) AS casequeries