[1.8.x] Fixed #24171 -- Fixed failure with complex aggregate query and expressions

The query used a construct of qs.annotate().values().aggregate() where
the first annotate used an F-object reference and the values() and
aggregate() calls referenced that F-object.

Also made sure the inner query's select clause is as simple as possible,
and made sure .values().distinct().aggreate() works correctly.

Backport of fb146193c4 from master

tests/aggregation_regress/tests.py

@@ -7,7 +7,9 @@ from operator import attrgetter
 
 from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import FieldError
-from django.db.models import F, Q, Avg, Count, Max, StdDev, Sum, Variance
+from django.db.models import (
+    F, Q, Avg, Count, Max, StdDev, Sum, Value, Variance,
+)
 from django.test import TestCase, skipUnlessDBFeature
 from django.test.utils import Approximate
 from django.utils import six
@@ -1129,6 +1131,14 @@ class AggregationTests(TestCase):
             'select__avg': Approximate(1.666, places=2),
         })
 
+    def test_annotate_distinct_aggregate(self):
+        # There are three books with rating of 4.0 and two of the books have
+        # the same price. Hence, the distinct removes one rating of 4.0
+        # from the results.
+        vals1 = Book.objects.values('rating', 'price').distinct().aggregate(result=Sum('rating'))
+        vals2 = Book.objects.aggregate(result=Sum('rating') - Value(4.0))
+        self.assertEqual(vals1, vals2)
+
 
 class JoinPromotionTests(TestCase):
     def test_ticket_21150(self):