[英]MySQL count with group by not returning correct result
我有一个正在尝试生成报告的票务系统。 我正在尝试获取每个用户涉及的票数。 有了第一个查询:
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;
我能够列出针对特定用户的票证,并且可以手动对其进行计数:
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的计数应该为11。其他大多数结果也不正确,它们似乎都比我预期的要少。
在子查询上使用GROUP BY / COUNT时,我做错什么了吗? 如何更改查询以获得所需的结果?
您是否只想汇总?
SELECT UserID, COUNT(*)
FROM dcscontact.ticketevents
WHERE EventDateTime BETWEEN '2016-06-22' AND '2016-06-23'
GROUP BY UserID;
如果对于一个给定用户,同一票证可以多次出现在数据中,则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;
要获取每个用户触摸的票证数量 ,让我们从正确的查询开始:
SELECT count(*) as N, UserID
FROM dcscontact.ticketevents
WHERE EventDateTime BETWEEN '2016-06-22' AND '2016-06-23'
GROUP BY UserID;
GROUP BY
子句应始终包括SELECT
子句中提到的所有非聚合列。 询问“票证ID和票证数量(每位用户)”是没有意义的!
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,而不是查询中使用的信息。
您还想知道一些关于TicketID
和EventDateTime
。 您不能要求输入“票证编号”,但可以获取第一张和最后一张票证。 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;
请注意,最早的时间可能不是最小的TicketID的时间。 要获取有关每个用户的第一张票证以及计数的所有信息,请结合以下两种信息来源:
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
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.