title: How to join to generate_series with SQLAlchemy
body: <p>I'm trying to bin some events by month.</p>
  
  <pre><code>date_list = func.generate_series(start, end, '1 month')
  
  db.session.query(func.count(Event.id)).join(date_list, true()).outerjoin(Event, Event.time==func.date(date_list)).all()
  </code></pre>
  
  <p>But I'm getting an error:</p>
  
  <p>NotSupportedError: (psycopg2.errors.FeatureNotSupported) set-returning functions are not allowed in JOIN conditions</p>
  
  <p>What's a simple example of using a series on the left side of the join with SQLAlchemy, and then using an aggregate like count?</p>