I have a model similar to the following:
class Review(models.Model): venue = models.ForeignKey(Venue, db_index=True) review = models.TextField()
This should work (using the same MySQL specific function you used):
Review.objects.filter(venue__pk=2) .extra({'date_created' : "date(datetime_created)"}) .values('date_created') .annotate(created_count=Count('id'))