从查询获取结果的空值

Question

我有这个疑问：

SELECT U.LOCATION,SUM(S.EXISTENCIA) AS Total 
FROM LOCATIONS U 
LEFT JOIN CANT_WAREHOUSE S ON U.LOCATION= S.LOCATION 
WHERE U.ENABLED= 1 
GROUP BY U.LOCATION 

和返回数据是这样的：

LOCATION | Total 
2A-1  | 566.0000000 
2A-2  | 14.0000000 
2A-3  | 1.0000000 
2A-4  | (null) 
2A-5  | 1.0000000 
2A-6  | (null) 
2A-7  | 6.0000000 
2B-1  | 560.0000000 
2B-2  | (null) 

有没有办法与“总”，让“LOCATION” = null使用子查询或类似的东西？

Answer 1

使用HAVING条款

SELECT U.LOCATION,SUM(S.EXISTENCIA) AS Total 
FROM LOCATIONS U 
LEFT JOIN CANT_WAREHOUSE S ON U.LOCATION= S.LOCATION 
    and U.ENABLED= 1 
GROUP BY U.LOCATION 
HAVING SUM(S.EXISTENCIA) IS NULL 

Answer 2

使用NOT EXISTS

SELECT U.LOCATION, 
     NULL AS Total 
FROM LOCATIONS U 
WHERE NOT EXISTS (SELECT 1 
        FROM CANT_WAREHOUSE S 
        WHERE U.LOCATION = S.LOCATION) 
     AND U.ENABLED = 1 
GROUP BY U.LOCATION