错误：“from 子句”中的未知列“catId”

Question

我已经在 WAMP 上运行了这个脚本，它运行良好。尝试上传时出现错误，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在 users.userId = forum_posts.userId GROUP BY catId
上加入用户 MySQL 错误：“from 子句”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。可能您未能准确地重新创建表架构。

Answer 2

可能是您的 catid 列在您加入的多个表中存在冲突，因此请使用带有列名的 alias

试试下面：

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