The query for creating a thread would be easy. What won't be easy is that unless you don't allow any other posts or threads, you're gonna have conflicts from the first user in terms of the threadid. (e.g. If user #2 signs up and there's already 5 threads, does threadid #2 get overwritten?) What would work better is if you added a field to the user table and stored the threadid for each user there. It might not correspond with the user's user #, but it would avoid the conflicts that are guaranteed to arise doing it the way you suggested.