我在WAMP上运行过这个脚本，它运行得很好。当我试图上传它时，我遇到了一个错误，不确定它的真正含义。
SELECT *, COUNT(DISTINCT forum_thread.threadId) AS 'threadTotal', COUNT(DISTINCT forum_posts.postId) AS 'postTotal'
FROM forum_cat
LEFT JOIN forum_posts USING (catId)
LEFT JOIN forum_thread USING (catId)
LEFT JOIN users ON users.userId = forum_posts.userId
GROUP BY forum_cat.catId
这是在WAMP中运行良好的SQL脚本；在线我得到以下错误
注意：查询：SELECT*，COUNT（DISTINCT forum_thread.threadId）为'threadTotal'，CONUNT（DISTINCT forum_posts.postId）为'spostTotal'FROM forum_cat LEFT JOIN forum_post USING（catId）LEFT JOINforum_tthread USING（catId）LEFTJOIN users.userId=forum_phosts.userId GROUP BY catId
MySQL错误："from clause"中的未知列"catId"
错误告诉您出了什么问题。没有这样的栏。可能您未能准确地重新创建表架构。
可能有catid列在多个表中，所以使用列名为的alias
试试下面的：
SELECT *, COUNT(DISTINCT ft.threadId) AS 'threadTotal', COUNT(DISTINCT fp.postId) AS 'postTotal'
FROM forum_cat as fc
LEFT JOIN forum_posts as fp USING(fp.catId)
LEFT JOIN forum_thread as ft USING(ft.catId)
LEFT JOIN users ON users.userId = fp.userId
GROUP BY fc.catId