选择MySQL中最常出现的值

我正在寻找一种方法来选择最常出现的值，例如，每个线程发布最多的人

SELECT MOST_OCCURRING(user_id) FROM thread_posts GROUP BY thread_id

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有没有一个好的方法可以做到这一点？

如果您想在每个线程的基础上进行计数，我认为您可以使用嵌套查询；先按线程分组，然后按用户分组：

SELECT thread_id AS tid,
    (SELECT user_id FROM thread_posts 
        WHERE thread_id = tid 
        GROUP BY user_id
        ORDER BY COUNT(*) DESC
        LIMIT 0,1) AS topUser
FROM thread_posts
GROUP BY thread_id

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如果你在“每组最大n”标签下检查问题，会有很多例子。但在这种情况下，您不需要定义如何处理关系-如果两个或多个用户具有相同的计数值，该怎么办

SELECT DISTINCT
       tp.thread_id,
       tp.user_id
  FROM THREAD_POSTS tp
  JOIN (SELECT t.thread_id,
               t.user_id,
               COUNT(t.user_id) AS occurrence,
               CASE
                 WHEN @thread != t.thread_id THEN @rownum := 1
                 ELSE @rownum := @rownum + 1
               END AS rank,
               @thread := t.thread_id
          FROM THREAD_POSTS t
          JOIN (SELECT @rownum := 0, @thread := -1) r
      GROUP BY t.thread_id, t.user_id
      ORDER BY t.thread_id, occurrence DESC) x ON x.thread_id = tp.thread_id
                                              AND x.user_id = tp.user_id
                                              AND x.rank = 1

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这将列出每个线程出现的用户id

SELECT thread_id, user_id, COUNT(*) as postings
FROM thread_posts
GROUP BY thread_id, user_id

但您只希望为每个线程选择顶级用户

SELECT thread_id, user_id, postings
FROM (
  SELECT thread_id, user_id, COUNT(*) as postings
  FROM thread_posts
  GROUP BY thread_id, user_id
)
HAVING postings = max(postings)

这相当于

SELECT thread_id, user_id, COUNT(*) as postings
FROM thread_posts
GROUP BY thread_id, user_id
HAVING postings = max(postings)

HAVING关键字通常与聚合操作一起使用，以挑选满足HAVING子句中条件的聚合输出行

HAVING子句不同于WHERE子句，其中HAVING子句过滤查询的结果输出。然而，WHERE子句过滤查询的输入数据。

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由于HAVING子句过滤查询的结果输出，因此它必须出现在ORDER BY和GROUP BY子句之后。

您想要每个线程一行的列表，并且相关的top POST user？不工作。运行此查询将提供空输出。mysql没有返回任何内容。