MySQL 通过不返回正确结果与组一起计数

Question

我有一个票务系统，我正在尝试运行对其进行报告。我正在尝试获取每个用户接触的票数。对于第一个查询：

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;

我能够列出特定用户接触的工单，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：

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;

我的计数不正确：

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。其他大多数结果也不正确，它们似乎都低于我的预期。

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

Answer 1

您只想要聚合吗？

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

如果对于给定的用户，同一张工单可以在数据中出现多次，那么 COUNT(DISTINCT) 更合适：

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

Answer 2

为了获得每个用户触摸的工单数量，让我们从一个正确的查询开始：

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

GROUP BY 子句应始终包含 SELECT 子句中提到的所有非聚合列。要求 "the ticket ID and the number of tickets (per user)"!

没有意义

另外，SQL 标准说 ORDER BY 不能应用于子查询。最好将 ORDER BY 视为查看输出的便利，而不是在查询中使用的信息。

您还想了解有关 TicketID 和 EventDateTime 的一些信息。你不能要"the id of the count of the tickets"，但你可以得到第一张和最后一张票。时间相同：

SELECT   count(*) as N
       , min(TicketID) as T1
       , max(TicketID) as Tn
       , min(EventDateTime) as E1
       , max(EventDateTime) as En
   , UserID
FROM dcscontact.ticketevents
WHERE EventDateTime BETWEEN '2016-06-22' AND '2016-06-23'
GROUP BY UserID;

注意最早的时间不一定是TicketID最小的时间。要获取有关每个用户的第一张票的所有信息以及计数，请加入两个信息来源：

select N.N, T.* 
from dcscontact.ticketevents as T
join (
    SELECT count(*) as N, min(TicketID) as T1, UserID
    FROM dcscontact.ticketevents
    WHERE EventDateTime BETWEEN '2016-06-22' AND '2016-06-23'
    GROUP BY UserID;
) as N
on  T.UserID = N.UserID 
and T.TicketID = N.TicketID
-- and maybe others, according to the key
order by EventDateTime DESC

MySQL 通过不返回正确结果与组一起计数

MySQL count with group by not returning correct result

mysql

sql

group-by

count

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