SQL - 从查询中获取单个数字的答案

Question

以下代码返回几个数字，标识参加三项以上活动的人员。

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

我希望答案是参与三项以上活动的人数，即“4”，而不是四个唯一数字。怎么办？

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pnr字段上的WHERE子句来唯一标识您的某个分组：

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

我的条款的顺序可能是错误的

Answer 3

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