title: How to make a subquery in sqlalchemy
body: <pre><code>SELECT *
  FROM Residents
  WHERE apartment_id IN (SELECT ID
                         FROM Apartments
                         WHERE postcode = 2000)
  </code></pre>
  
  <p>I'm using sqlalchemy and am trying to execute the above query. I haven't been able to execute it as raw  SQL using <code>db.engine.execute(sql)</code> since it complains that my relations doesn't exist... But I succesfully query my database using this format: <code>session.Query(Residents).filter_by(???)</code>.
  I cant not figure out how to build my wanted query with this format, though.</p>