Question

我在WAMP上运行了这个脚本，它工作正常。在尝试上传时，我收到了一个错误，并且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中正常运行的SQL脚本;在线我收到以下错误

注意：查询：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用户ON users.userId = forum_posts.userId GROUP BY catId
MySQL错误：'from clause'
中的未知列'catId'

Answer 1

错误告诉你出了什么问题。没有这样的专栏。可能你没能完全重新创建表模式。

Answer 2

您可能有catid列在多个表格中加入了相互冲突的表格，因此请使用alias列名称

尝试以下：

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

错误：'from子句'中的未知列'catId'

2 个答案: