title: SQL query generated by django F expression
body: <p>Does anyone know the actual query generated by django when you use F expression?</p>
  
  <p>What will the generated query be for the example mentioned in the doc: <a href="https://docs.djangoproject.com/en/2.1/ref/models/expressions/#f-expressions" rel="nofollow noreferrer">https://docs.djangoproject.com/en/2.1/ref/models/expressions/#f-expressions</a></p>
  
  <pre><code>from django.db.models import F
  
  reporter = Reporters.objects.get(name='Tintin')
  reporter.stories_filed = F('stories_filed') + 1
  reporter.save()
  </code></pre>
  
  <p>I tried viewing the query generated using:</p>
  
  <pre><code>from django.db import connection
  logging.info('[----- DEBUG -----] Query -1: %s', connection.queries[-1])
  logging.info('[----- DEBUG -----] Query -2: %s', connection.queries[-2])
  logging.info('[----- DEBUG -----] Query -3: %s', connection.queries[-3])
  </code></pre>
  
  <p>but I don't see any query on the my model/table.</p>
  
  <p>Anyone know how to figure this out?</p>