[英]How do I select a row with max count doing a group by
I have a table posts
with columns ( id
, user_name
, thread_id
). 我有一个表posts
列( id
, user_name
, thread_id
)。
A user can submit multiple posts for a thread. 用户可以为一个线程提交多个帖子。 thread to post is one to many. 发布线程是一对多的。
I need to find out who submitted max posts per thread. 我需要找出谁每个线程最多提交了帖子。 So the result would be Max(Count)
, user_name
, thread_id
WHERE there will be only one row per thread_id. 因此结果将是Max(Count)
, user_name
, thread_id
,其中每个thread_id只有一行。
The table is too huge so I wanted to get the query optimized as much as I could. 该表太大,因此我想尽可能优化查询。
You can try with the group by
and having
clauses: 您可以group by
having
子句来尝试使用该group by
:
select t.user_name, t.thread_id , count(*) as max_count
from tbl t
group by t.user_name, t.thread_id
having count(*) = ( select count(*) as ttl
from tbl
where thread_id = t.thread_id
group by user_name
order by ttl desc
limit 1 )
select user_name, thread_id, count(*) as max
from tbl t
group by user_name, thread_id
having count(*) = (
select count(*) as cnt /* most posts per user per thread */
from tbl
group by user_name, thread_id
order by cnt desc
limit 1
)
Easy workaround for system that don't have limit
is: 对于没有limit
系统,简单的解决方法是:
select user_name, thread_id, count(*) as max
from tbl t
group by user_name, thread_id
having count(*) = (
select max(cnt) from (
select count(*) as cnt /* most posts per user per thread */
from tbl
group by user_name, thread_id
) m
)
Try this.. SELECT p.user_name, p.thread_id FROM post p GROUP BY p.user_name,p.thread_id HAVING COUNT(p.thread_id) = (SELECT MAX(threadtypecount) FROM (SELECT thread_id, COUNT([user_name]) AS threadtypecount FROM post GROUP BY thread_id) T1) 试试这个。.选择p.user_name,p.thread_id FROM post p GROUP BY p.user_name,p.thread_id HAVING COUNT(p.thread_id)=(SELECT MAX(threadtypecount)FROM(SELECT thread_id,COUNT([user_name])AS从发帖组(thread_id)发出的threadtypecount)T1)
hope this helps.. 希望这可以帮助..
Suppose you have a table posts
with fields id
, user_name
& thread_id
. 假设您有一个表posts
其中包含字段id
, user_name
和thread_id
。 If you want to query which user has posted the most posts on a specific thread and the total number of his posts from a table, you can achieve that with this MySQL query: 如果要查询哪个用户在特定线程上发布的帖子最多,以及从表中发布的帖子总数,则可以通过以下MySQL查询来实现:
SELECT user_name, thread_id, count(thread_id)
FROM posts WHERE thread_id=1 GROUP BY user_name
ORDER BY count(thread_id) DESC LIMIT 1;
It will return only one row... 它只会返回一行...
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