[英]How to get maximum row of each group?
I have a database in which people submit votes for people in different places. 我有一个数据库,人们可以在该数据库中为不同地方的人投票。 At a given time, I want to find out who has the most votes at each place. 在给定的时间,我想找出在每个地方投票最多的人。 (A person can be voted at two different places) (一个人可以在两个不同的地方投票)
This is the SQL I have so far: 这是我到目前为止拥有的SQL:
SELECT placeId, userVotedId, cnt
FROM
(SELECT uvo.userVotedId, p.placeId, count(*) as cnt
FROM users as u, users_votes as uvo, places as p
WHERE u.userId = uvo.userVotedId
AND p.placeId = uvo.placeId
GROUP BY userVotedId, placeId)
AS RESULT
which gives me this result: 这给了我这个结果:
Now, these are the rows I REALLY want: 现在,这些是我真正想要的行:
What's missing in my query so I can get this? 我的查询中缺少什么,所以我可以得到这个?
I want one result per place. 我想要每个地方一个结果。 So I should see only distinct placeIds, with the userVotedId who received the most votes. 因此,我应该只能看到截然不同的placeIds,其中userVotedId得票最多。
In the event of a tie, a random winner will do! 如果出现平局,随机赢家会赢!
Seems like you need one more aggregate.
似乎您还需要一个聚合。
Use the
MAX()
aggregate on your
cnt
value and
GROUP BY placeId, userVotedId
:
在您的
cnt
值和
GROUP BY placeId, userVotedId
上使用
MAX()
聚合:
SELECT placeId, userVotedId, max(cnt) FROM ( SELECT uvo.userVotedId, p.placeId, count(*) as cnt FROM users as u INNER JOIN users_votes as uvo ON u.userId = uvo.userVotedId INNER JOIN places as p ON p.placeId = uvo.placeId GROUP BY userVotedId, placeId ) AS RESULT GROUP BY placeId, userVotedId
Note: I changed your query to use
JOIN
syntax instead of the commas between the tables.
注意:我将查询更改为使用
JOIN
语法而不是表之间的逗号。
Edit, based on your comment the following should work: 编辑,根据您的评论,以下应该起作用:
select total.uservotedid,
total.placeid,
total.cnt
from
(
SELECT uvo.userVotedId, p.placeId, count(*) as cnt
FROM users as u
INNER JOIN users_votes as uvo
ON u.userId = uvo.userVotedId
INNER JOIN places as p
ON p.placeId = uvo.placeId
GROUP BY userVotedId, placeId
) total
inner join
(
select max(cnt) Mx, placeid
from
(
SELECT uvo.userVotedId, p.placeId, count(*) as cnt
FROM users as u
INNER JOIN users_votes as uvo
ON u.userId = uvo.userVotedId
INNER JOIN places as p
ON p.placeId = uvo.placeId
GROUP BY userVotedId, placeId
) mx
group by placeid
) src
on total.placeid = src.placeid
and total.cnt = src.mx
See SQL Fiddle with Demo 参见带有演示的SQL Fiddle
The result is: 结果是:
| USERVOTEDID | PLACEID | CNT |
-------------------------------
| 65 | 11 | 1 |
| 67 | 13 | 1 |
| 67 | 25 | 1 |
| 67 | 51 | 2 |
Edit #2, if you want a random number returned if there is a tie, then you can use user variables: 编辑#2,如果希望在有平局的情况下返回随机数,则可以使用用户变量:
select uservotedid,
placeid,
cnt
from
(
select total.uservotedid,
total.placeid,
total.cnt,
@rownum := case when @prev = total.placeid then @rownum+1 else 1 end rownum,
@prev := total.placeid pplaceid
from
(
SELECT uvo.userVotedId, p.placeId, count(*) as cnt
FROM users as u
INNER JOIN users_votes as uvo
ON u.userId = uvo.userVotedId
INNER JOIN places as p
ON p.placeId = uvo.placeId
GROUP BY userVotedId, placeId
) total
inner join
(
select max(cnt) Mx, placeid
from
(
SELECT uvo.userVotedId, p.placeId, count(*) as cnt
FROM users as u
INNER JOIN users_votes as uvo
ON u.userId = uvo.userVotedId
INNER JOIN places as p
ON p.placeId = uvo.placeId
GROUP BY userVotedId, placeId
) mx
group by placeid
) src
on total.placeid = src.placeid
and total.cnt = src.mx
order by total.placeid, total.uservotedid
) src
where rownum = 1
order by placeid, uservotedid
SELECT placeId, userVotedId, MAX(cnt)
FROM (SELECT uvo.userVotedId, p.placeId, count(*) AS cnt
FROM users as u, users_votes as uvo, places as p
WHERE u.userId = uvo.userVotedId AND p.placeId = uvo.placeId
GROUP BY userVotedId, placeId) AS RESULT
GROUP BY placeId
Similar Question - SQL query max(), count() 相似的问题-SQL查询max(),count()
For simplicity, I called your query Test: 为简单起见,我将您的查询称为Test:
SELECT *
FROM Test T JOIN (
SELECT t.placeId, Max(t.cnt) maxcnt
FROM Test t
GROUP BY t.placeId) T2 ON T.placeId = T2.placeId and T.cnt = T2.maxcnt
BTW -- Test = : 顺便说一句-测试=:
SELECT uvo.userVotedId, p.placeId, count(*) as cnt
FROM users as u
INNER JOIN users_votes as uvo
ON u.userId = uvo.userVotedId
INNER JOIN places as p
ON p.placeId = uvo.placeId
GROUP BY userVotedId, placeId
Good luck. 祝好运。
--EDIT -- as requested, here is the final code: -编辑-根据要求,这是最终代码:
SELECT *
FROM (SELECT uvo.userVotedId, p.placeId, count(*) AS cnt
FROM users as u, users_votes as uvo, places as p
WHERE u.userId = uvo.userVotedId AND p.placeId = uvo.placeId
GROUP BY userVotedId, placeId) T JOIN (
SELECT t.placeId, Max(t.cnt) maxcnt
FROM (SELECT uvo.userVotedId, p.placeId, count(*) AS cnt
FROM users as u, users_votes as uvo, places as p
WHERE u.userId = uvo.userVotedId AND p.placeId = uvo.placeId
GROUP BY userVotedId, placeId) t
GROUP BY t.placeId) T2 ON T.placeId = T2.placeId and T.cnt = T2.maxcnt
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