title: Django INNER JOIN with GROUP BY queryset
body: <p>How can I get the following SQL queryset in Django?</p>
  
  <pre><code>SELECT abbreviation, COUNT(tat_value) FROM t_tat 
  INNER JOIN t_tests ON t_tat.test_id = t_tests.test
  GROUP BY test
  </code></pre>
  
  <p>These are my class models:</p>
  
  <pre><code>class tat(models.Model):
      test = models.ForeignKey(tests)
      tat_value
      ...
  
  class tests(models.Model):
      test = models.IntegerField(primary_key=True, default=0)
      ...
  </code></pre>