如何選擇最大計數的行進行分組

Question

我有一個表posts列（ id ， user_name ， thread_id ）。
用戶可以為一個線程提交多個帖子。 發布線程是一對多的。

我需要找出誰每個線程最多提交了帖子。 因此結果將是Max(Count) ， user_name ， thread_id ，其中每個thread_id只有一行。

該表太大，因此我想盡可能優化查詢。

Answer 1

您可以group by having子句來嘗試使用該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
)

對於沒有limit系統，簡單的解決方法是：

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

試試這個。.選擇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從發帖組（thread_id）發出的threadtypecount）T1）

希望這可以幫助..

Answer 4

假設您有一個表posts其中包含字段id ， user_name和thread_id 。 如果要查詢哪個用戶在特定線程上發布的帖子最多，以及從表中發布的帖子總數，則可以通過以下MySQL查詢來實現：

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;

它只會返回一行...