How to execute GROUP BY ... COUNT or SUM in Django ORM?

Question

Prologue:

This often raises the question in SO:

• Django Model Group by
• Django equivalent for count and group
• How to query like GROUP BY in django?
• How to use ORM for equivalent SQL query, group and join?

I made an example on SO Documentation, but since the Documentation will be closed on August 8, 2017, I will follow up on the proposal for this widely accepted and discussed meta-answer and convert my example into a standalone answer.

Of course, I would be more than happy to see any other approach.

---

Question:

Suppose the model:

class Books(models.Model):
    title  = models.CharField()
    author = models.CharField()
    price = models.FloatField()

How can I execute the following queries for this model using Django ORM:

• GROUP BY ... COUNT:

  SELECT author, COUNT(author) AS count
  FROM myapp_books GROUP BY author
  

• GROUP BY ... SUM:

  SELECT author,  SUM (price) AS total_price
  FROM myapp_books GROUP BY author
  

Answer 1

SQL- GROUP BY... COUNT GROUP BY... SUM Django ORM annotate(), values(), django.db.models Count Sum order_by():

• GROUP BY... COUNT:

  from django.db.models import Count
  
  result = Books.objects.values('author')
                        .order_by('author')
                        .annotate(count=Count('author'))
  

  : author count:

    author    | count
  ------------|-------
   OneAuthor  |   5
  OtherAuthor |   2
     ...      |  ...
  

• GROUP BY... SUM:

  from django.db.models import Sum
  
   result = Books.objects.values('author')
                         .order_by('author')
                         .annotate(total_price=Sum('price'))
  

  : author total_price:

    author    | total_price
  ------------|-------------
   OneAuthor  |    100.35
  OtherAuthor |     50.00
      ...     |      ...