Refs #23622 -- Added tests to ensure ordering is retained for distinct on fields subqueries.

The ticket was already fixed by
b68212f539f206679580afbfd008e7d329c9cd31.

Thanks to Beauhurst for commissioning the work on this ticket.

tests/queries/tests.py

@@ -3732,3 +3732,71 @@ class TestTicket24605(TestCase):
             ).order_by('pk'),
             [i1, i2, i3], lambda x: x
         )
+
+
+class Ticket23622Tests(TestCase):
+    @skipUnlessDBFeature('can_distinct_on_fields')
+    def test_ticket_23622(self):
+        """
+        Make sure __pk__in and __in work the same for related fields when
+        using a distinct on subquery.
+        """
+        a1 = Ticket23605A.objects.create()
+        a2 = Ticket23605A.objects.create()
+        c1 = Ticket23605C.objects.create(field_c0=0.0)
+        Ticket23605B.objects.create(
+            modela_fk=a1, field_b0=123,
+            field_b1=datetime.date(2013, 1, 6),
+            modelc_fk=c1,
+        )
+        Ticket23605B.objects.create(
+            modela_fk=a1, field_b0=23,
+            field_b1=datetime.date(2011, 6, 6),
+            modelc_fk=c1,
+        )
+        Ticket23605B.objects.create(
+            modela_fk=a1, field_b0=234,
+            field_b1=datetime.date(2011, 9, 2),
+            modelc_fk=c1,
+        )
+        Ticket23605B.objects.create(
+            modela_fk=a1, field_b0=12,
+            field_b1=datetime.date(2012, 9, 15),
+            modelc_fk=c1,
+        )
+        Ticket23605B.objects.create(
+            modela_fk=a2, field_b0=567,
+            field_b1=datetime.date(2014, 3, 1),
+            modelc_fk=c1,
+        )
+        Ticket23605B.objects.create(
+            modela_fk=a2, field_b0=76,
+            field_b1=datetime.date(2011, 3, 3),
+            modelc_fk=c1,
+        )
+        Ticket23605B.objects.create(
+            modela_fk=a2, field_b0=7,
+            field_b1=datetime.date(2012, 10, 20),
+            modelc_fk=c1,
+        )
+        Ticket23605B.objects.create(
+            modela_fk=a2, field_b0=56,
+            field_b1=datetime.date(2011, 1, 27),
+            modelc_fk=c1,
+        )
+        qx = (
+            Q(ticket23605b__pk__in=Ticket23605B.objects.order_by('modela_fk', '-field_b1').distinct('modela_fk'))
+            & Q(ticket23605b__field_b0__gte=300)
+        )
+        qy = (
+            Q(ticket23605b__in=Ticket23605B.objects.order_by('modela_fk', '-field_b1').distinct('modela_fk'))
+            & Q(ticket23605b__field_b0__gte=300)
+        )
+        self.assertEqual(
+            set(Ticket23605A.objects.filter(qx).values_list('pk', flat=True)),
+            set(Ticket23605A.objects.filter(qy).values_list('pk', flat=True))
+        )
+        self.assertQuerysetEqual(
+            Ticket23605A.objects.filter(qx),
+            [a2], lambda x: x
+        )