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
35042	Queryset count does not work after union when annotations on aggregation are unused.	Marcin	Simon Charette	"While upgrading to Django 4 I've found a bug with `count()` which can be replicated using the following code. Notice that evaluating the queryset works fine, the issue is that for some reason, when counting django is not including `total_count` column from the second queryset in the query and this is causing union to fail. In Django 3 the code works fine and produces a correct SQL. I've attached an example project which can be used to reproduce the bug, with command `tox -e ALL`.

models.py
{{{#!python
class Foo(models.Model):
    name = models.TextField()

class Bar(models.Model):
    foo = models.ForeignKey(Foo, on_delete=models.CASCADE)
    count = models.IntegerField()
}}}

tests.py
{{{#!python
qs1 = Foo.objects.all().annotate(
    _count=models.Sum('bar__count')
).values('name').annotate(
    total_count=models.F('_count')
).values('name', 'total_count')

qs2 = Bar.objects.all().annotate(
    name=models.F('foo__name'),
    total_count=models.Value(0, output_field=models.IntegerField())
).values('name', 'total_count')

self.assertEqual(list(qs1.union(qs2, all=True)), [])
self.assertEqual(qs1.union(qs2, all=True).count(), 0)
}}}

Exception thrown in Django 4+

{{{
Traceback (most recent call last):
  File ""/home/user/foo/bar/tests.py"", line 21, in test_recreate_bug
    self.assertEqual(qs1.union(qs2, all=True).count(), 0)
  File ""/home/user/foo/.tox/django5/lib/python3.10/site-packages/django/db/models/query.py"", line 618, in count
    return self.query.get_count(using=self.db)
  File ""/home/user/foo/.tox/django5/lib/python3.10/site-packages/django/db/models/sql/query.py"", line 616, in get_count
    return obj.get_aggregation(using, {""__count"": Count(""*"")})[""__count""]
  File ""/home/user/foo/.tox/django5/lib/python3.10/site-packages/django/db/models/sql/query.py"", line 602, in get_aggregation
    result = compiler.execute_sql(SINGLE)
  File ""/home/user/foo/.tox/django5/lib/python3.10/site-packages/django/db/models/sql/compiler.py"", line 1562, in execute_sql
    cursor.execute(sql, params)
  File ""/home/user/foo/.tox/django5/lib/python3.10/site-packages/django/db/backends/utils.py"", line 79, in execute
    return self._execute_with_wrappers(
  File ""/home/user/foo/.tox/django5/lib/python3.10/site-packages/django/db/backends/utils.py"", line 92, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File ""/home/user/foo/.tox/django5/lib/python3.10/site-packages/django/db/backends/utils.py"", line 100, in _execute 
    with self.db.wrap_database_errors:
  File ""/home/user/foo/.tox/django5/lib/python3.10/site-packages/django/db/utils.py"", line 91, in __exit__ 
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File ""/home/user/foo/.tox/django5/lib/python3.10/site-packages/django/db/backends/utils.py"", line 105, in _execute 
    return self.cursor.execute(sql, params)
  File ""/home/user/foo/.tox/django5/lib/python3.10/site-packages/django/db/backends/sqlite3/base.py"", line 328, in execute
    return super().execute(query, params)
django.db.utils.OperationalError: SELECTs to the left and right of UNION ALL do not have the same number of result columns
}}}"	Bug	closed	Database layer (models, ORM)	4.2	Normal	fixed		Simon Charette	Ready for checkin	1	0	0	0	0	0