[3.0.x] Fixed #30771 -- Fixed exact lookup against queries with selected columns.

Use pre-existing select fields (and thereby GROUP BY fields) from
subquery if they were specified, instead of always defaulting to pk.

Thanks Aur Saraf for the report and Simon Charette for guidance.

Backport of 0719edcd5fed56157ffb3323a8f634aa5e8f9a80 from master

3 files changed, 17 insertions, 3 deletions

diff --git a/AUTHORS b/AUTHORS
index 460bb9a7df..87011bf1e8 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -384,6 +384,7 @@ answer newbie questions, and generally made Django that much better:
     James Bennett <james@b-list.org>
     James Murty
     James Tauber <jtauber@jtauber.com>
+    James Timmins <jameshtimmins@gmail.com>
     James Wheare <django@sparemint.com>
     Jannis Leidel <jannis@leidel.info>
     Janos Guljas
diff --git a/django/db/models/lookups.py b/django/db/models/lookups.py
index 105dc93251..2683d8971a 100644
--- a/django/db/models/lookups.py
+++ b/django/db/models/lookups.py
@@ -262,9 +262,9 @@ class Exact(FieldGetDbPrepValueMixin, BuiltinLookup):
         from django.db.models.sql.query import Query
         if isinstance(self.rhs, Query):
             if self.rhs.has_limit_one():
-                # The subquery must select only the pk.
-                self.rhs.clear_select_clause()
-                self.rhs.add_fields(['pk'])
+                if not self.rhs.has_select_fields:
+                    self.rhs.clear_select_clause()
+                    self.rhs.add_fields(['pk'])
             else:
                 raise ValueError(
                     'The QuerySet value for an exact lookup must be limited to '
diff --git a/tests/lookup/tests.py b/tests/lookup/tests.py
index a603824c0d..1958b995b2 100644
--- a/tests/lookup/tests.py
+++ b/tests/lookup/tests.py
@@ -5,6 +5,7 @@ from operator import attrgetter
 
 from django.core.exceptions import FieldError
 from django.db import connection
+from django.db.models import Max
 from django.db.models.expressions import Exists, OuterRef
 from django.db.models.functions import Substr
 from django.test import TestCase, skipUnlessDBFeature
@@ -956,3 +957,15 @@ class LookupTests(TestCase):
             ),
         )
         self.assertEqual(qs.get(has_author_alias_match=True), tag)
+
+    def test_exact_query_rhs_with_selected_columns(self):
+        newest_author = Author.objects.create(name='Author 2')
+        authors_max_ids = Author.objects.filter(
+            name='Author 2',
+        ).values(
+            'name',
+        ).annotate(
+            max_id=Max('id'),
+        ).values('max_id')
+        authors = Author.objects.filter(id=authors_max_ids[:1])
+        self.assertEqual(authors.get(), newest_author)