MySQL通过不返回正确的结果来计数

Question

我有一个票务系统，我正在尝试在其上运行报告。我试图让每个用户接触的票数。使用第一个查询：

SELECT * FROM (
SELECT TicketID, UserID, EventDateTime
FROM dcscontact.ticketevents
WHERE EventDateTime BETWEEN '2016-06-22' AND '2016-06-23'
ORDER BY EventDateTime DESC) x
WHERE UserID=80
GROUP BY TicketID;

我能够列出为特定用户触碰的工单，并且可以手动计算它们：

TicketID    UserID  EventDateTime
99168       80      6/22/2016 13:21
99193       80      6/22/2016 7:42
99213       80      6/22/2016 13:02
99214       80      6/22/2016 6:30
99221       80      6/22/2016 6:57
99224       80      6/22/2016 7:48
99226       80      6/22/2016 6:27
99228       80      6/22/2016 8:49
99229       80      6/22/2016 8:53
99232       80      6/22/2016 9:18
99237       80      6/22/2016 13:08

但是当我尝试删除 WHERE UserID= 语句并尝试将其用作子查询时，如下所示：

SELECT UserID, COUNT(*) as count FROM (
    SELECT * FROM (
    SELECT TicketID, UserID, EventDateTime
    FROM dcscontact.ticketevents
    WHERE EventDateTime BETWEEN '2016-06-22' AND '2016-06-23'
    ORDER BY EventDateTime DESC) x
    GROUP BY TicketID) y
GROUP BY UserID;

我得到不正确的计数：

UserID  count
9       2
28      1
31      1
42      1
80      5
95      1
99      6
108     4
116     12
117     26
123     24

如您所见，UserID 80 的计数应该是 11。大多数其他结果也不正确，它们似乎都比我预期的要低。

在子查询上使用 GROUP BY/COUNT 时我做错了什么吗？如何更改我的查询以获得我想要的结果？

Answer 1

你只是想要一个聚合吗？

SELECT UserID, COUNT(*)
FROM dcscontact.ticketevents
WHERE EventDateTime BETWEEN '2016-06-22' AND '2016-06-23'
GROUP BY UserID;

如果同一个工单可以多次出现在给定用户的数据中，COUNT(DISTINCT)则更合适：

SELECT UserID, COUNT(DISTINCT TicketID)
FROM dcscontact.ticketevents
WHERE EventDateTime BETWEEN '2016-06-22' AND '2016-06-23'
GROUP BY UserID;