如何避免SQL中的子查詢重復？

Question

我想要用途A的最低價格和用途B的最高價格，而且我還按區域對物品進行分組。

SELECT ZONE, MIN_PRICE, MAX_PRICE --,LEFT_ZONE
  FROM 
  (SELECT MIN(PRICE) AS MIN_PRICE , ZONE  AS LEFT_ZONE
    FROM MYTABLE 
    WHERE PURPOSE = 'A'
      AND SOMETHING = 'SOMEVALUE'
    GROUP BY ZONE 
   )
    FULL OUTER JOIN 
  (SELECT MAX(PRICE) AS MAX_PRICE, ZONE_CD  
    FROM MYTABLE 
    WHERE PURPOSE = 'B'
      AND SOMETHING = 'SOMEVALUE'
    GROUP BY ZONE 
   )
  ON LEFT_ZONE = ZONE 

該查詢提供了我想要的輸出，但是由於兩個原因，我不喜歡它：

1）我想要

FROM MYTABLE 
WHERE SOMETHING = 'SOMEVALUE'

只能被調用一次。

2）當行來自我的完整外部聯接中的右表時，我得到ZONE null。

我該如何解決這些問題。

查詢中還有其他問題嗎？

Answer 1

您是否嘗試過使用CASE表達式來獲取此信息：

select zone,
  min(case when PURPOSE = 'A' then price end) min_price,
  max(case when PURPOSE = 'B' then price end) max_price
from MYTABLE 
where SOMETHING = 'SOMEVALUE'
group by zone

Answer 2

嘗試這個：

  SELECT 
    ZONE, 
    SUM (CASE WHEN PURPOSE = 'A' THEN MIN(PRICE) ELSE 0 END) AS MIN_PRICE,
    SUM (CASE WHEN PURPOSE = 'B' THEN MAX(PRICE) ELSE 0 END) AS MAX_PRICE
  FROM 
    MYTABLE 
  WHERE 
    SOMETHING = 'SOMEVALUE'
  GROUP BY 
    ZONE 

或任何小的變化