SQL连接QUERY多个表和SELECT

Question

I build the following query,

        SELECT
        posts.id,
        posts.useraid,
        posts.useradn,
        posts.title,
        posts.createdate,
        posts.forumid,
        posts.type,
        posts.totalreplys,
        users.photo AS creatorphoto
    FROM posts
    JOIN users ON(users.id = posts.useraid)
    WHERE posts.forumid IN(
        SELECT subscribe.forumid AS fsub
        FROM subscribe  
        WHERE subscribe.useraid = '$myid'
    ) AND
    posts.forumid IN(
        SELECT forums.id
        FROM forums
        WHERE forums.relatedto=fsub
    )
    AND posts.type='post' 
    ORDER BY posts.timee DESC LIMIT 20

The code works perfectly without this part

AND
    posts.forumid IN(
        SELECT forums.id
        FROM forums
        WHERE forums.relatedto=fsub
    )

But, I need the query to select all posts from all forums he subscribe to, including the subforums posts.

Answer 1

'fsub' has no scope here, it doesn't really even exist at this point in your query:

posts.forumid IN(
    SELECT forums.id
    FROM forums
    WHERE forums.relatedto=fsub
)

You need to use a UNION I believe.