Fixed #31094 -- Included columns referenced by subqueries in GROUP BY on aggregations.

Thanks Johannes Hoppe for the report.

Regression in fb3f034f1c.

Co-authored-by: Mariusz Felisiak <felisiak.mariusz@gmail.com>

django/db/models/expressions.py

@@ -1040,7 +1040,7 @@ class Subquery(Expression):
     def get_group_by_cols(self, alias=None):
         if alias:
             return [Ref(alias, self)]
-        return []
+        return self.query.get_external_cols()
 
 
 class Exists(Subquery):

django/db/models/sql/compiler.py

@@ -109,7 +109,14 @@ class SQLCompiler:
         # Note that even if the group_by is set, it is only the minimal
         # set to group by. So, we need to add cols in select, order_by, and
         # having into the select in any case.
+        ref_sources = {
+            expr.source for expr in expressions if isinstance(expr, Ref)
+        }
         for expr, _, _ in select:
+            # Skip members of the select clause that are already included
+            # by reference.
+            if expr in ref_sources:
+                continue
             cols = expr.get_group_by_cols()
             for col in cols:
                 expressions.append(col)
@@ -399,7 +406,7 @@ class SQLCompiler:
             return self.quote_cache[name]
         if ((name in self.query.alias_map and name not in self.query.table_map) or
                 name in self.query.extra_select or (
-                    name in self.query.external_aliases and name not in self.query.table_map)):
+                    self.query.external_aliases.get(name) and name not in self.query.table_map)):
             self.quote_cache[name] = name
             return name
         r = self.connection.ops.quote_name(name)

django/db/models/sql/query.py

@@ -157,7 +157,8 @@ class Query(BaseExpression):
         # Sometimes the query contains references to aliases in outer queries (as
         # a result of split_exclude). Correct alias quoting needs to know these
         # aliases too.
-        self.external_aliases = set()
+        # Map external tables to whether they are aliased.
+        self.external_aliases = {}
         self.table_map = {}     # Maps table names to list of aliases.
         self.default_cols = True
         self.default_ordering = True
@@ -855,8 +856,11 @@ class Query(BaseExpression):
                 if alias == old_alias:
                     table_aliases[pos] = new_alias
                     break
-        self.external_aliases = {change_map.get(alias, alias)
-                                 for alias in self.external_aliases}
+        self.external_aliases = {
+            # Table is aliased or it's being changed and thus is aliased.
+            change_map.get(alias, alias): (aliased or alias in change_map)
+            for alias, aliased in self.external_aliases.items()
+        }
 
     def bump_prefix(self, outer_query):
         """
@@ -1030,19 +1034,23 @@ class Query(BaseExpression):
         for key, value in clone.annotations.items():
             resolved = value.resolve_expression(query, *args, **kwargs)
             if hasattr(resolved, 'external_aliases'):
-                resolved.external_aliases.update(clone.alias_map)
+                resolved.external_aliases.update(clone.external_aliases)
             clone.annotations[key] = resolved
         # Outer query's aliases are considered external.
-        clone.external_aliases.update(
-            alias for alias, table in query.alias_map.items()
-            if (
-                isinstance(table, Join) and table.join_field.related_model._meta.db_table != alias
-            ) or (
-                isinstance(table, BaseTable) and table.table_name != table.table_alias
-            )
+        for alias, table in query.alias_map.items():
+            clone.external_aliases[alias] = (
+                (isinstance(table, Join) and table.join_field.related_model._meta.db_table != alias) or
+                (isinstance(table, BaseTable) and table.table_name != table.table_alias)
             )
         return clone
 
+    def get_external_cols(self):
+        exprs = chain(self.annotations.values(), self.where.children)
+        return [
+            col for col in self._gen_cols(exprs)
+            if col.alias in self.external_aliases
+        ]
+
     def as_sql(self, compiler, connection):
         sql, params = self.get_compiler(connection=connection).as_sql()
         if self.subquery:
@@ -1635,12 +1643,16 @@ class Query(BaseExpression):
         return targets, joins[-1], joins
 
     @classmethod
-    def _gen_col_aliases(cls, exprs):
+    def _gen_cols(cls, exprs):
         for expr in exprs:
             if isinstance(expr, Col):
-                yield expr.alias
+                yield expr
             else:
-                yield from cls._gen_col_aliases(expr.get_source_expressions())
+                yield from cls._gen_cols(expr.get_source_expressions())
+
+    @classmethod
+    def _gen_col_aliases(cls, exprs):
+        yield from (expr.alias for expr in cls._gen_cols(exprs))
 
     def resolve_ref(self, name, allow_joins=True, reuse=None, summarize=False):
         if not allow_joins and LOOKUP_SEP in name:
@@ -1733,7 +1745,7 @@ class Query(BaseExpression):
             lookup = lookup_class(pk.get_col(query.select[0].alias),
                                   pk.get_col(alias))
             query.where.add(lookup, AND)
-            query.external_aliases.add(alias)
+            query.external_aliases[alias] = True
 
         condition, needed_inner = self.build_filter(
             ('%s__in' % trimmed_prefix, query),

docs/releases/3.0.2.txt

@@ -9,4 +9,5 @@ Django 3.0.2 fixes several bugs in 3.0.1.
 Bugfixes
 ========
 
-* ...
+* Fixed a regression in Django 3.0 that didn't include columns referenced by a
+  ``Subquery()`` in the ``GROUP BY`` clause (:ticket:`31094`).

tests/aggregation/tests.py

@@ -1172,3 +1172,23 @@ class AggregateTestCase(TestCase):
             Exists(long_books_qs),
         ).annotate(total=Count('*'))
         self.assertEqual(dict(has_long_books_breakdown), {True: 2, False: 3})
+
+    def test_aggregation_subquery_annotation_related_field(self):
+        publisher = Publisher.objects.create(name=self.a9.name, num_awards=2)
+        book = Book.objects.create(
+            isbn='159059999', name='Test book.', pages=819, rating=2.5,
+            price=Decimal('14.44'), contact=self.a9, publisher=publisher,
+            pubdate=datetime.date(2019, 12, 6),
+        )
+        book.authors.add(self.a5, self.a6, self.a7)
+        books_qs = Book.objects.annotate(
+            contact_publisher=Subquery(
+                Publisher.objects.filter(
+                    pk=OuterRef('publisher'),
+                    name=OuterRef('contact__name'),
+                ).values('name')[:1],
+            )
+        ).filter(
+            contact_publisher__isnull=False,
+        ).annotate(count=Count('authors'))
+        self.assertSequenceEqual(books_qs, [book])