[Django] #31580: Expect to get SELECT DISTINCT ON after UNION of 2 annotated QuerySet

[Django]

#31580: Expect to get SELECT DISTINCT ON after UNION of 2 annotated QuerySet
-------------------------------------+-------------------------------------
               Reporter:  Sielc      |          Owner:  nobody
                   Type:  Bug        |         Status:  new
              Component:  Database   |        Version:  3.0
  layer (models, ORM)                |       Keywords:  orm, distinct,
               Severity:  Normal     |  annotate, union
           Triage Stage:             |      Has patch:  0
  Unreviewed                         |
    Needs documentation:  0          |    Needs tests:  0
Patch needs improvement:  0          |  Easy pickings:  0
                  UI/UX:  0          |
-------------------------------------+-------------------------------------
 After using
 - .annotate() on 2 different querysets
 - and then .union()
 - .distinct() will not affect the queryset

 {{{
     def setUp(self) -> None:
         user = self.get_or_create_admin_user()

         Sample.h.create(user, name="Sam1")
         Sample.h.create(user, name="Sam2 acid")
         Sample.h.create(user, name="Sam3")
         Sample.h.create(user, name="Sam4 acid")

         Sample.h.create(user, name="Dub")
         Sample.h.create(user, name="Dub")
         Sample.h.create(user, name="Dub")

         self.user = user

     def test_union_annotated_diff_distinct(self):
         qs = Sample.objects.filter(user=self.user)
         qs1 = qs.filter(name='Dub').annotate(rank=Value(0,
 IntegerField()))
         qs2 = qs.filter(name='Sam1').annotate(rank=Value(1,
 IntegerField()))
         qs = qs1.union(qs2)
         qs = qs.order_by('name').distinct('name')  # THIS DISTINCT
 DONESN'T WORK
         self.assertEqual(qs.count(), 2)
 }}}

 expected to get wrapped union
 {{{
     SELECT DISTINCT ON (siebox_sample.name) * FROM (SELECT ... UNION
 SELECT ...) AS siebox_sample
 }}}

-- 
Ticket URL: <https://code.djangoproject.com/ticket/31580>
Django <https://code.djangoproject.com/>
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