避免子查詢

Question

研究員， 我有一個查詢，如下所示：

SELECT A.ID, B.ID, (HUGE SUBQUERY) as HS 
FROM TABLE_A JOIN TABLE_B ON A.ID = B.ID 
WHERE (HUGE SUBQUERY) > 0 

我想避免重複子查詢。 有什麼辦法重寫我何至於像

WHERE HS > 0 

或者，我必須把我的子查詢轉換爲連接？

Answer 1

你可以使用一個CTE：

WITH cteHS AS (
    SELECT xxx AS Value 
     FROM Huge Subquery 
) 
SELECT A.ID, B.ID, cteHS.Value as HS 
    FROM TABLE_A, cteHS 
     JOIN TABLE_B ON A.ID = B.ID 
    WHERE cteHS.Value > 0 

Answer 2

看一下使用條款：

WITH HS AS (Huge subquery) 

SELECT A.ID, B.ID, HS 
FROM TABLE_A JOIN TABLE_B ON A.ID = B.ID 
WHERE HS > 0 

OR

SELECT * 
FROM 
(
    SELECT A.ID, B.ID, (HUGE SUBQUERY) as HS 
    FROM TABLE_A JOIN TABLE_B ON A.ID = B.ID 
) 
WHERE HS > 0