使用與GROUPING HAVING SETS

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 

我得到的結果如下

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

如果國家已經得到了只有一個城市的記錄，我可以得到結果如下使用HAVING

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 

• GROUPING(City) = 0 if City當前正在分組的字段之一。
• 相反，當GROUPING(City) = 1則City報告爲NULL。

這意味着我們總是包含提到City的行（不是NULL）。

對於其他行，其中GROUPING(City) = 1又名City IS NULL，那麼如果多於一個City已彙總到結果中，那麼我們只包含該行。