将HAVING与GROUPING SETS一起使用

Question

我的sql字符串如下

SELECT Country, City, COUNT(*) AS [Count]
FROM   CountriesAndCities
GROUP  BY GROUPING SETS ( ( Country, City ), ( Country) )     
ORDER  BY Country, City 

我得到如下结果

Country     City        CountryCount
----------  ----------  ------------
France      NULL        4 
France      Paris       4           
Spain       NULL        6 
Spain       Barcelona   3           
Spain       Madrid      3   

如果某个国家/地区只有一个城市记录，那么使用HAVING可以获得以下结果吗？

Country     City        CountryCount
----------  ----------  ------------
France      Paris       4           
Spain       NULL        6 
Spain       Barcelona   3           
Spain       Madrid      3  

Answer 1

SELECT Country, City, COUNT(*) AS [Count]
FROM   CountriesAndCities
GROUP  BY GROUPING SETS ( ( Country, City ), ( Country) )
HAVING GROUPING(City) = 0
    OR COUNT(DISTINCT City) > 1
ORDER  BY Country, City

• 如果City是当前分组依据的字段之一，则GROUPING(City) = 0 。
• 相反，当GROUPING(City) = 1 City被报告为NULL 。

这意味着我们总是包括提到City的行（不是NULL ）。

对于其他行，其中GROUPING(City) = 1 aka City IS NULL ，则仅在将多个City聚合到结果中的情况下才包括该行。