Queryset annotation mixing aggregate and subquery doesn't GROUP BY outer column references.

[Igor Pejic]

After trying to migrate from 2.2. to 3.0, we experience a problem with the translation of queries in PostgreSQL which used to work in 2.2.

A breaking test is shown in: ​https://github.com/igorpejic/django/pull/1/files

From investigation this is related to: https://code.djangoproject.com/ticket/31094
and it seems the regression was introduced in: ​https://github.com/django/django/commit/fb3f034f1c63160c0ff13c609acd01c18be12f80

It seems that the combination of the "double OuterRef" with the "Case" logic is causing the problem.

Query looks like:

        books_with_same_name_as_country = Book.objects.filter(
            id__in=Subquery(
                Book.objects.filter(
                    name=OuterRef(OuterRef('country__name')),
                ).values('id')
            )
        ).values('id')[:1]
        books_breakdown = Publisher.objects.annotate(total_books=Case(
            When(
                num_awards__gte=2,
                then=Subquery(books_with_same_name_as_country, IntegerField())
            ),
            When(
                num_awards__lt=0,
                then=Count('country__publishers')
            ),
        ))

Stack trace:

======================================================================
ERROR: test_group_by_subquery_annotation_with_conditional (aggregation.tests.AggregateTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/igor/django-repo/django/db/backends/utils.py", line 86, in _execute
    return self.cursor.execute(sql, params)
psycopg2.errors.GroupingError: subquery uses ungrouped column "aggregation_country.name" from outer query
LINE 1: ..."id" FROM "aggregation_book" U0 WHERE U0."name" = "aggregati...
                                                             ^


The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/igor/django-repo/django/test/testcases.py", line 1229, in skip_wrapper
    return test_func(*args, **kwargs)
  File "/home/igor/django-repo/tests/aggregation/tests.py", line 1299, in test_group_by_subquery_annotation_with_conditional
    self.assertEqual(books_breakdown.get(id=self.p1.id).total_books, 1)
  File "/home/igor/django-repo/django/db/models/query.py", line 411, in get
    num = len(clone)
  File "/home/igor/django-repo/django/db/models/query.py", line 258, in __len__
    self._fetch_all()
  File "/home/igor/django-repo/django/db/models/query.py", line 1261, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/home/igor/django-repo/django/db/models/query.py", line 57, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
  File "/home/igor/django-repo/django/db/models/sql/compiler.py", line 1154, in execute_sql
    cursor.execute(sql, params)
  File "/home/igor/django-repo/django/db/backends/utils.py", line 68, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "/home/igor/django-repo/django/db/backends/utils.py", line 77, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/home/igor/django-repo/django/db/backends/utils.py", line 86, in _execute
    return self.cursor.execute(sql, params)
  File "/home/igor/django-repo/django/db/utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/home/igor/django-repo/django/db/backends/utils.py", line 86, in _execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: subquery uses ungrouped column "aggregation_country.name" from outer query
LINE 1: ..."id" FROM "aggregation_book" U0 WHERE U0."name" = "aggregati...
                                                             ^

Full query 2.2:

SELECT "aggregation_regress_publisher"."id",
       "aggregation_regress_publisher"."name",
       "aggregation_regress_publisher"."num_awards",
       "aggregation_regress_publisher"."country_id",
       CASE
           WHEN "aggregation_regress_publisher"."num_awards" >= 2 THEN
                  (SELECT V0."id"
                   FROM "aggregation_regress_book" V0
                   WHERE V0."id" IN
                       (SELECT U0."id"
                        FROM "aggregation_regress_book" U0
                        WHERE U0."name" = ("aggregation_regress_country"."name")
                        ORDER BY U0."name" ASC)
                   ORDER BY V0."name" ASC
                   LIMIT 1)
           WHEN "aggregation_regress_publisher"."num_awards" < 0 THEN COUNT(T3."id")
           ELSE NULL
       END AS "total_books"
FROM "aggregation_regress_publisher"
INNER JOIN "aggregation_regress_country" ON ("aggregation_regress_publisher"."country_id" = "aggregation_regress_country"."id")
LEFT OUTER JOIN "aggregation_regress_publisher" T3 ON ("aggregation_regress_country"."id" = T3."country_id")
GROUP BY "aggregation_regress_publisher"."id",
  (SELECT V0."id"
   FROM "aggregation_regress_book" V0
   WHERE V0."id" IN
       (SELECT U0."id"
        FROM "aggregation_regress_book" U0
        WHERE U0."name" = ("aggregation_regress_country"."name")
        ORDER BY U0."name" ASC)
   ORDER BY V0."name" ASC
   LIMIT 1)

Full query 3.0:

SELECT "aggregation_publisher"."id",
       "aggregation_publisher"."name",
       "aggregation_publisher"."num_awards",
       "aggregation_publisher"."duration",
       "aggregation_publisher"."country_id",
       CASE
           WHEN "aggregation_publisher"."num_awards" >= 2 THEN
                  (SELECT V0."id"
                   FROM "aggregation_book" V0
                   WHERE V0."id" IN
                       (SELECT U0."id"
                        FROM "aggregation_book" U0
                        WHERE U0."name" = "aggregation_country"."name")
                   LIMIT 1)
           WHEN "aggregation_publisher"."num_awards" < 0 THEN COUNT(T3."id")
           ELSE NULL
       END AS "total_books"
FROM "aggregation_publisher"
INNER JOIN "aggregation_country" ON ("aggregation_publisher"."country_id" = "aggregation_country"."id")
LEFT OUTER JOIN "aggregation_publisher" T3 ON ("aggregation_country"."id" = T3."country_id")
GROUP BY "aggregation_publisher"."id"

[Simon Charette]

That looks like another case of #31094 but generalized for expressions that mix aggregates and subqueries.

Case.get_group_by_cols() defers to BaseExpression.get_group_by_cols() when it has cases and the latter immediately returns self ​when it contains aggregates.

Igor, could you include the SQL that uses to be generated and what the new one looks like?