Php 在MySQL中为留言板获取正确的最大结果，但不是正确的计数值

这是我第一次来这里。我正在尝试使用

PHP

和

MySQL

构建一个留言板（论坛）。我想在

PHP

中显示一个包含以下信息的表：

一列显示所有当前论坛

另一列显示每个线程和帖子的总数 论坛

显示最新创建的线程的最后一列

这是我的查询，它返回正确的最新线程，但不是正确的计数：

SELECT 
       forums.*,
       threads.thread_id,
       threads.thread_topic,
       threads.user_id,
       users.user_name, 
       threads.thread_date, 
       COUNT(DISTINCT threads.thread_id) AS thread_count,
       COUNT(DISTINCT posts.post_id) AS post_count
   FROM forums 
   LEFT OUTER JOIN threads
      ON forums.forum_id = threads.forum_id
      AND threads.thread_date = 
         (SELECT MAX(threads.thread_date) AS last_topic
             FROM threads 
             WHERE forums.forum_id = threads.forum_id)
   LEFT JOIN users 
      ON users.user_id = threads.user_id
   LEFT JOIN posts 
      ON threads.thread_id = posts.thread_id
   GROUP BY forums.forum_id

这些是帖子和帖子计数的结果，它只计算每个论坛最新帖子中的帖子和帖子：

post count  thread count
    -             -
    7             1
    1             1
    1             1
    1             1
    0             0

SELECT 
       COUNT(DISTINCT posts.post_id) AS post_count, 
       COUNT(DISTINCT threads.thread_id) AS thread_count
   FROM forums 
   LEFT OUTER JOIN threads 
      ON threads.forum_id = forums.forum_id
   LEFT JOIN posts 
      ON threads.thread_id = posts.thread_id
   GROUP BY forums.forum_id;

此查询获取每个论坛的正确帖子和线程数：

post count  thread count
    -             -
    7             1
    1             1
    1             1
    1             1
    0             0

SELECT 
       COUNT(DISTINCT posts.post_id) AS post_count, 
       COUNT(DISTINCT threads.thread_id) AS thread_count
   FROM forums 
   LEFT OUTER JOIN threads 
      ON threads.forum_id = forums.forum_id
   LEFT JOIN posts 
      ON threads.thread_id = posts.thread_id
   GROUP BY forums.forum_id;

每个论坛的帖子和线程数结果应为：

post count  thread count
        -             -
        7             1
        1             1
        3             2
        1             1
        0             0

我是否可以组合这两个查询，或者修复第一个查询，从而获得正确的输出

请在您的建议中使用下表：

用户、线程、论坛、帖子

我是新来的

PHP

和

MySQL

，如果这样做不对，我很抱歉

---

非常感谢你的帮助

由于

和threads.threaddate=（选择MAX（threads.threaddate）…

条件，您只计算最新线程。您需要加入一个子查询，以获取每个论坛中最新线程的行。请参阅以了解如何编写子查询。是的，我理解。我只是不确定如何正确设置子查询的格式。谢谢你的链接。是的，看起来很有效。感谢您抽出时间写出解决方案！

SELECT
    forums.*,
    counts.thread_count,
    counts.post_count,
    threads.*,           -- last thread
    users.*              -- user of last thread
FROM forums
LEFT JOIN (
    SELECT 
        forums.forum_id,
        COUNT(DISTINCT threads.thread_id) AS thread_count,
        COUNT(DISTINCT posts.post_id) AS post_count
    FROM forums 
    LEFT JOIN threads ON threads.forum_id = forums.forum_id
    LEFT JOIN posts ON posts.thread_id = threads.thread_id
    GROUP BY forums.forum_id
) counts ON counts.forum_id = forums.forum_id
LEFT JOIN (
    SELECT
        forums.forum_id,
        threads.thread_id,
    FROM forums
    JOIN threads ON forums.forum_id = threads.forum_id
    AND threads.thread_date = 
        (SELECT MAX(threads.thread_date) AS last_topic
            FROM threads 
            WHERE forums.forum_id = threads.forum_id)
) last_thread ON last_thread.forum_id = forums.forum_id
LEFT JOIN threads ON threads.thread_id = last_thread.thread_id
LEFT JOIN users ON users.user_id = threads.user_id