Fixed #26434 -- Removed faulty clearing of ordering field when missing from explicit grouping.

Co-authored-by: Simon Charette <charette.s@gmail.com>

django/db/models/sql/query.py

@@ -534,7 +534,8 @@ class Query(BaseExpression):
             # Queries with distinct_fields need ordering and when a limit is
             # applied we must take the slice from the ordered query. Otherwise
             # no need for ordering.
-            inner_query.clear_ordering(force=False)
+            if inner_query.orderby_issubset_groupby:
+                inner_query.clear_ordering(force=False)
             if not inner_query.distinct:
                 # If the inner query uses default select and it has some
                 # aggregate annotations, then we must make sure the inner
@@ -2338,6 +2339,33 @@ class Query(BaseExpression):
         else:
             self.default_ordering = False
 
+    @property
+    def orderby_issubset_groupby(self):
+        if self.extra_order_by:
+            # Raw SQL from extra(order_by=...) can't be reliably compared
+            # against resolved OrderBy/Col expressions. Treat as not a subset.
+            return False
+        if self.group_by in (None, True):
+            # There is either no aggregation at all (None), or the group by
+            # is generated automatically from model fields (True), in which
+            # case the order by is necessarily a subset of them.
+            return True
+        if not self.order_by:
+            # Although an empty set is always a subset, there's no point in
+            # clearing ordering when there isn't any. Avoid the clone() below.
+            return True
+        # Don't pollute the original query (might disrupt joins).
+        q = self.clone()
+        order_by_set = {
+            (
+                order_by.resolve_expression(q)
+                if hasattr(order_by, "resolve_expression")
+                else F(order_by).resolve_expression(q)
+            )
+            for order_by in q.order_by
+        }
+        return order_by_set.issubset(self.group_by)
+
     def clear_ordering(self, force=False, clear_default=True):
         """
         Remove any ordering settings if the current query allows it without

tests/aggregation_regress/tests.py

@@ -171,6 +171,24 @@ class AggregationTests(TestCase):
         for attr, value in kwargs.items():
             self.assertEqual(getattr(obj, attr), value)
 
+    def test_count_preserve_group_by(self):
+        # new release of the same book
+        Book.objects.create(
+            isbn="113235613",
+            name=self.b4.name,
+            pages=self.b4.pages,
+            rating=4.0,
+            price=Decimal("39.69"),
+            contact=self.a5,
+            publisher=self.p3,
+            pubdate=datetime.date(2018, 11, 3),
+        )
+        qs = Book.objects.values("contact__name", "publisher__name").annotate(
+            publications=Count("id")
+        )
+        self.assertEqual(qs.order_by("id").count(), len(qs.order_by("id")))
+        self.assertEqual(qs.extra(order_by=["id"]).count(), len(qs.order_by("id")))
+
     def test_annotation_with_value(self):
         values = (
             Book.objects.filter(