[Admin]

I don't really understand what you are trying to do, but anyhow this code will give you the userid,username,postsperday and posts of the user with the highest posts per day ranking:

$user=$DB_site->query_first("SELECT userid,username,posts,(posts/((UNIX_TIMESTAMP(NOW())-joindate)/86400)) AS postsperday FROM user ORDER BY postsperday DESC");

Have fun.