id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
34527	Unexpected behavior with division in aggregation	Egor R	nobody	"I came across an unexpected behavior (code taken from a real project, and the models are renamed):

{{{
django.__version__
# '3.2.18'

MyModel.objects.all().annotate(
    score=Sum(""relatedmodel__points"", output_field=FloatField(), filter=Q(relatedmodel__owner=user),)
    / Count(""relatedmodel__id"", filter=Q(relatedmodel__owner=user)),
).values_list(""score"", flat=True)
# <QuerySet [None, 10.0, 8.0, None, 9.0, None]>

MyModel.objects.all().annotate(
    score=Sum(""relatedmodel__points"", output_field=FloatField(), filter=Q(relatedmodel__owner=user),)
).values_list(""score"", flat=True)
# <QuerySet [None, 40.0, 35.0, None, 37.0, None]>

MyModel.objects.all().annotate(
    score=Count(""relatedmodel__id"", filter=Q(relatedmodel__owner=user),),
).values_list(""score"", flat=True)
# <QuerySet [0, 4, 4, 0, 4, 0]>
}}}

Since we're specifying `output_field=FloatField()` for `Sum`, I expected to get 10, 8.75 and 9.25 as the results of the first query, but I'm getting 10.0/8.0/9.0.
I looked into SQL code generated by the query - there's no casting of `Sum` to float there, so it's somewhat understandable why it is happening. But, shouldn't Django cast `Sum` to float in SQL?

Explicitly casting `Count` as `FloatField` works, though:
{{{
MyModel.objects.all().annotate(
    score=Sum(""relatedmodel__points"", output_field=FloatField(), filter=Q(relatedmodel__owner=user),)
    / Cast(Count(""relatedmodel__id"", filter=Q(relatedmodel__owner=user)), FloatField())
).values_list(""score"", flat=True)
# <QuerySet [None, 10.0, 8.75, None, 9.25, None]>
}}}

Relevant snippets of the models:

{{{
class MyModel(models.Model):
    ...

class RelatedModel(models.Model):
    points = models.PositiveSmallIntegerField(
        ""description"", default=10, null=True, blank=True
    )
    mymodel = models.ForeignKey(""myapp.MyModel"", on_delete=models.CASCADE)
    owner = models.ForeignKey(User, on_delete=models.CASCADE)
    ...
}}}

I created an MRE, will attach it to the ticket.
Tested on Postgres 12 (real project) and 15 (MRE).

PS Real project uses django-tenants, and I included it in the MRE as I tried to track down the bug. Can retest and create MRE without django-tenants if needed."	Bug	closed	Database layer (models, ORM)	3.2	Normal	invalid			Unreviewed	0	0	0	0	0	0