I have a relatively simple subset of tables in my database for tracking something called sessions. These are academic sessions (think offerings of a particular program). The tables to represent a sessions information are:

sessions
  session_terms
    session_subjects
      session_mark_item_info
        session_marks

All of these tables have their own primary keys, and are like a tree, in that sessions have terms, terms have subjects, subjects have mark items, etc. So each on would have at least its "parent's" foreign key.

My question is, design wise is it a good idea to include the sessions primary key in the other tables as a foreign key to easily select related session items, or is that too much redundency?

If I include the session foreign key (or all parent foreign keys from tables up the heirarchy) in all the tables, I can easily select all the marks for a session. As an example, something like

SELECT mark FROM session_marks WHERE sessionID=...

If I don't, then I would have to combine selects with something like

WHERE something IN (SELECT...

Which approach is "more correct" or efficient?

Thanks in advance!