#31580: Expect to get SELECT DISTINCT ON after UNION of 2 annotated QuerySet
-------------------------------------+-------------------------------------
     Reporter:  Sielc                |                    Owner:  nobody
         Type:  Bug                  |                   Status:  new
    Component:  Database layer       |                  Version:  3.0
  (models, ORM)                      |
     Severity:  Normal               |               Resolution:
     Keywords:  orm, distinct,       |             Triage Stage:
  annotate, union                    |  Unreviewed
    Has patch:  0                    |      Needs documentation:  0
  Needs tests:  0                    |  Patch needs improvement:  0
Easy pickings:  0                    |                    UI/UX:  0
-------------------------------------+-------------------------------------
Description changed by Sielc:

Old description:

> 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
> }}}

New description:

 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 DOESN'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#comment:1>
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