[2.1.x] Fixed #29416 -- Removed unnecesary subquery from GROUP BY clause on MySQL when using a RawSQL annotation.

Regression in 1d070d027c.
Backport of 4ab1f559e8 from master

django/db/models/sql/compiler.py

@@ -157,7 +157,9 @@ class SQLCompiler:
                 }
                 expressions = [pk] + [
                     expr for expr in expressions
-                    if expr in having or getattr(expr, 'alias', None) not in pk_aliases
+                    if expr in having or (
+                        getattr(expr, 'alias', None) is not None and expr.alias not in pk_aliases
+                    )
                 ]
         elif self.connection.features.allows_group_by_selected_pks:
             # Filter out all expressions associated with a table's primary key

docs/releases/2.0.6.txt

@@ -14,3 +14,6 @@ Bugfixes
 
 * Fixed detection of custom URL converters in included patterns
   (:ticket:`29415`).
+
+* Fixed a regression that added an unnecessary subquery to the ``GROUP BY``
+  clause on MySQL when using a ``RawSQL`` annotation (:ticket:`29416`).

tests/annotations/tests.py

@@ -6,6 +6,7 @@ from django.db.models import (
     BooleanField, CharField, Count, DateTimeField, ExpressionWrapper, F, Func,
     IntegerField, NullBooleanField, Q, Sum, Value,
 )
+from django.db.models.expressions import RawSQL
 from django.db.models.functions import Length, Lower
 from django.test import TestCase, skipUnlessDBFeature
 
@@ -322,6 +323,17 @@ class NonAggregateAnnotationTestCase(TestCase):
         for publisher in publishers.filter(pk=self.p1.pk):
             self.assertEqual(publisher['book__rating'], publisher['total'])
 
+    @skipUnlessDBFeature('allows_group_by_pk')
+    def test_rawsql_group_by_collapse(self):
+        raw = RawSQL('SELECT MIN(id) FROM annotations_book', [])
+        qs = Author.objects.values('id').annotate(
+            min_book_id=raw,
+            count_friends=Count('friends'),
+        ).order_by()
+        _, _, group_by = qs.query.get_compiler(using='default').pre_sql_setup()
+        self.assertEqual(len(group_by), 1)
+        self.assertNotEqual(raw, group_by[0])
+
     def test_defer_annotation(self):
         """
         Deferred attributes can be referenced by an annotation,