如何选择最大计数的行进行分组

Question

我有一个表posts列（ id ， user_name ， thread_id ）。
用户可以为一个线程提交多个帖子。 发布线程是一对多的。

我需要找出谁每个线程最多提交了帖子。 因此结果将是Max(Count) ， user_name ， thread_id ，其中每个thread_id只有一行。

该表太大，因此我想尽可能优化查询。

Answer 1

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 )

Answer 2

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
)

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
)

Answer 3

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）

希望这可以帮助..

Answer 4

假设您有一个表posts其中包含字段id ， user_name和thread_id 。 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;

它只会返回一行...