title: Django query: more on weekends or weekdays
body: <p>Suppose I have two models:</p>
  
  <pre><code>class User(models.Model):
      name = CharField(max_length=42)
  
  class Action(models.Model):
      user = models.ForeignKey(User)
      timestamp = models.DateTimeField(auto_now_add=True)
  </code></pre>
  
  <p>How can I find all users who have more actions on weekends (sunday and saturday) than on other days of week and vice versa?</p>
  
  <p>Edit: I don't need to check this condition for one user, that would be easy. I need to select all users who have one of these conditions hold true.</p>