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

Question

Prologue:

This is a question arising often in SO:

I have composed an example on SO Documentation but since the Documentation will get shut down on August 8, 2017, I will follow the suggestion of this widely upvoted and discussed meta answer and transform my example to a self-answered post.

Of course, I would be more than happy to see any different approach as well!!

Question:

Assume the model:

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

How can I perform the following queries on that model utilizing 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

Asked By: John Moutafis

||

Source

Answer 1

We can perform a GROUP BY ... COUNT or a GROUP BY ... SUM SQL equivalent queries on Django ORM, with the use of annotate(), values(), the django.db.models‘s Count and Sum methods respectfully and optionally the order_by() method:

GROUP BY … COUNT:

 from django.db.models import Count

 result = Books.objects.values('author')
                       .order_by('author')
                       .annotate(count=Count('author'))

Now result contains a dictionary with two keys: author and 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'))

Now result contains a dictionary with two columns: author and total_price:

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

UPDATE 13/04/2021

As @dgw points out in the comments, in the case that the model uses a meta option to order rows (ex. ordering), the order_by() clause is paramount for the success of the aggregation!

Answered By: John Moutafis

Answer 2

in group by SUM() you can get almost two dict objects like

inv_data_tot_paid =Invoice.objects.aggregate(total=Sum('amount', filter=Q(status = True,month = m,created_at__year=y)),paid=Sum('amount', filter=Q(status = True,month = m,created_at__year=y,paid=1)))
print(inv_data_tot_paid)
##output -{'total': 103456, 'paid': None}

do not try out more than two query filter otherwise, you will get error like

Answered By: Prashan Basantia

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

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