SQL - 從查詢中作爲單個數字獲取答案

Question

以下代碼返回一對數字，標識參與三個以上活動的人員。

SELECT pnr 
FROM Participates 
GROUP BY pnr 
HAVING count(activities)>3; 

我希望答案是參加超過三個活動的人數，即「4」，而不是四個唯一的數字。該怎麼辦？

Answer 1

Access支持派生表。

SELECT COUNT(*) AS NumberOfParticipants FROM 
(
SELECT pnr 
    FROM Participates 
GROUP BY pnr 
HAVING count(activities)>3 
) T 

Answer 2

您需要在pnr領域的WHERE子句來唯一地標識您的分組之一：

SELECT COUNT(pnr) 
FROM Participates 
GROUP BY pnr 
WHERE pnr = 'whatever' 
HAVING COUNT(activities)>3 

我的條款的順序可能是錯誤

Answer 3

Select Count(Distinct pnr) 
From Participates 
Having Count(activities) > 3