Question

我目前正在为我的学校项目构建自己的论坛，此查询列出了所有论坛类别，但是我有问题检查是否有用户未读取的主题/主题，然后将论坛类别标记为未读消息。

它在子查询中的'字段列表'中显示“未知列'forum_category.id'”我已经检查了子查询的几个例子，从我看到的我应该能够访问 forum_category.id 并在子查询中使用它？我不知道我在这一点上做错了什么...

非常感谢帮助！

    SELECT forum_category.id 
   , root.name AS root_name 
   , subcat.name AS subcat_name 
   , subcat.id AS subcat_id 
   , subcat.description AS subcat_description 
   , subcat.safe_url AS subcat_safe_url 
   , topics.topic_id 
   , topics.topic_safe_url 
   , topics.topic_title 
   , topics.last_post_time 
   , topics.topic_last_poster_name 
   , topics.topic_last_poster_id 
   , (
        SELECT 
            posts_read.last_read_time
        FROM 
            forum_topics a 
        LEFT JOIN
            forum_posts_read AS posts_read ON 
                posts_read.last_read_time > a.last_post_time 
                AND posts_read.last_read_time > 1321004546  
                AND posts_read.topic_id = a.topic_id 
                AND posts_read.user_id = 1 
                AND a.forum_id = forum_category.id 
        LIMIT 1) AS last_read_time 
FROM forum_category AS root 
LEFT JOIN 
    forum_category AS subcat ON subcat.parent_id = root.id  
LEFT JOIN 
    forum_topics AS topics ON topics.forum_id = subcat.id 
LEFT JOIN 
    forum_topics AS t2 ON t2.forum_id = subcat.id AND t2.last_post_time > topics.last_post_time 
WHERE 
    root.parent_id = 0 AND t2.forum_id IS NULL 
ORDER BY 
    root_name, subcat_name

我知道尝试了这个，但它只检查每个类别中的第一个主题/主题...

SELECT root.name AS root_name 
   , subcat.name AS subcat_name 
   , subcat.id AS subcat_id 
   , subcat.description AS subcat_description 
   , subcat.safe_url AS subcat_safe_url 
   , topics.topic_id 
   , topics.topic_safe_url 
   , topics.topic_title 
   , topics.last_post_time 
   , topics.topic_last_poster_name 
   , topics.topic_last_poster_id 
   , posts_read.last_read_time 
FROM forum_category AS root 
LEFT JOIN 
    forum_category AS subcat ON subcat.parent_id = root.id  
LEFT JOIN 
    forum_topics AS topics ON topics.forum_id = subcat.id 
LEFT JOIN 
    forum_topics AS t2 ON t2.forum_id = subcat.id AND t2.last_post_time > topics.last_post_time 
LEFT JOIN
    forum_posts_read AS posts_read ON 
        posts_read.last_read_time > topics.last_post_time 
        AND posts_read.last_read_time > ?  
        AND posts_read.topic_id = topics.topic_id 
        AND posts_read.user_id = ? 
        AND topics.forum_id = subcat.id 
WHERE 
    root.parent_id = 0 AND t2.forum_id IS NULL 
ORDER BY 
    root_name, subcat_name

谁知道这会很难...我的意思是我想做的事情很简单:(

Answer 1

表。我相信你的问题在于表的别名。你告诉引擎不要使用forum_category而是使用ROOT或subcat。所以SQL不知道一个forum_Category（它没有在“FROM”中看到该表。外部select也存在同样的问题。也将它改为root。

SELECT root.id 
   , root.name AS root_name 
   , subcat.name AS subcat_name 
   , subcat.id AS subcat_id 
   , subcat.description AS subcat_description 
   , subcat.safe_url AS subcat_safe_url 
   , topics.topic_id 
   , topics.topic_safe_url 
   , topics.topic_title 
   , topics.last_post_time 
   , topics.topic_last_poster_name 
   , topics.topic_last_poster_id 
   , (
        SELECT 
            posts_read.last_read_time
        FROM 
            forum_topics a 
        LEFT JOIN
            forum_posts_read AS posts_read ON 
                posts_read.last_read_time > a.last_post_time 
                AND posts_read.last_read_time > 1321004546  
                AND posts_read.topic_id = a.topic_id 
                AND posts_read.user_id = 1 
                AND a.forum_id = Root.id 
        LIMIT 1) AS last_read_time 
FROM forum_category AS root 
LEFT JOIN 
    forum_category AS subcat ON subcat.parent_id = root.id  
LEFT JOIN 
    forum_topics AS topics ON topics.forum_id = subcat.id 
LEFT JOIN 
    forum_topics AS t2 ON t2.forum_id = subcat.id AND t2.last_post_time > topics.last_post_time 
WHERE 
    root.parent_id = 0 AND t2.forum_id IS NULL 
ORDER BY 
    root_name, subcat_name

子查询中的未知列为什么？

1 个答案: