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
34858	Bug in output field handling	Toan Vuong	nobody	"Tested on Django 4.2.4.

My model is defined like this:

```
class Choice(models.Model):
    choice_text = models.CharField(max_length=200)
    votes = models.IntegerField(default=0)
    arbitrary_num = models.PositiveIntegerField(default=1)
    arbitrary_num2 = models.PositiveIntegerField(default=2)
```

And this query is failing with Oracle (Tested on 19.3), but not Postgres:

```
s = Coalesce(F('arbitrary_num') + F('arbitrary_num2'),
                 Value(0, PositiveIntegerField()))
case = Case(
        When(arbitrary_num=1, then=Value(1, PositiveIntegerField())),
        default=s,
        output_field=PositiveIntegerField()
)

qs = Choice.objects.annotate(ss=case)
list(qs)

#qs = Choice.objects.annotate(s=s)
#list(qs)

```

The error (It's talking about the `Coalesce` function not having an `output_field`):

```
django.core.exceptions.FieldError: Expression contains mixed types: IntegerField, PositiveIntegerField. You must set output_field.
```

I believe the error is correct, because I think adding two `PositiveIntegerField()` seem to result in an `IntegerField`, so we *need* to specify an `output_field` on `Coalesce` to tell Django the proper output type to use. My question is that this seem to only throw an error in Oracle, and *not* Postgres. So it seems like the behavior on Postgres is unexpected? Somehow, the `Case` statement swallows the exception in Postgres and generates correct result. This can be demonstrated by the queryset where the `Coalesce` function is annotated directly without a case statement -- in this case, both Postgres and Oracle fails with the above error.

Note that this used to work prior to 4.2 (we upgraded from 3.x, where this used to work), although again I believe it was incorrect behavior and an `output_field` *should* be specified.

"	Uncategorized	new	Uncategorized	4.2	Normal				Unreviewed	0	0	0	0	0	0