title: Design considerations to using Foreign Key as Primary Key
body: <p>Are there any general design considerations (good/bad/neutral) for using a foreign key of one table as the primary key in another table?</p>
  
  <p>For example, assume the following tables as part of a film catalogue:</p>
  
  <pre><code>titles
  ------
   id
  
  
  episodes
  --------
   title_id (PK/FK)
  </code></pre>
  
  <p>Episodes could obviously be done with both an id and a title_id, where id would be the PK and title_id would be UNIQUE, but since title_id is already unique, and, technically, identifies the episode, would there be anything to consider in just using it as the PK?  What about in general?  What design considerations can you see to this?</p>
  
  <p>Thanks for your thoughts!</p>