[Django] #30209: Union with group by don't generate correct Subquery

[Django]

#30209: Union with group by don't generate correct Subquery
-------------------------------------+-------------------------------------
               Reporter:  Nikolas    |          Owner:  nobody
                   Type:             |         Status:  new
  Uncategorized                      |
              Component:  Database   |        Version:  1.11
  layer (models, ORM)                |
               Severity:  Normal     |       Keywords:  union, group by
           Triage Stage:             |      Has patch:  0
  Unreviewed                         |
    Needs documentation:  0          |    Needs tests:  0
Patch needs improvement:  0          |  Easy pickings:  0
                  UI/UX:  0          |
-------------------------------------+-------------------------------------
 reopen: https://code.djangoproject.com/ticket/30203

 Simplified for example:
 have simple query


 {{{
     qs1: QuerySet = User.objects.filter(id__gt=10)

     qs1 = qs1.values('is_active').annotate(id=Count('pk'))
 }}}

 generate:

 {{{
 SELECT "suser_customuser"."is_active",
        COUNT("suser_customuser"."id") AS "id"
 FROM "suser_customuser"
 WHERE "suser_customuser"."id" > 10
 GROUP BY "suser_customuser"."is_active"
 }}}

 all correct, now i wont use union

 {{{
     qs1: QuerySet = User.objects.filter(id__gt=10)
     qs2: QuerySet = User.objects.filter(id__lt=10)

     qs1 = qs1.values('is_active').annotate(id=Count('pk'))

 }}}

 now get not correct SQL:

 {{{
   (SELECT "suser_customuser"."is_active",
           "suser_customuser"."id"
    FROM "suser_customuser"
    WHERE "suser_customuser"."id" > 10)
 UNION
   (SELECT "suser_customuser"."is_active",
           "suser_customuser"."id"
    FROM "suser_customuser"
    WHERE "suser_customuser"."id" < 10)
 }}}


 expected:

 {{{
 select *
 from
   ((SELECT "suser_customuser"."is_active",
           "suser_customuser"."id"
    FROM "suser_customuser"
    WHERE "suser_customuser"."id" > 10)
 UNION
   (SELECT "suser_customuser"."is_active",
           "suser_customuser"."id"
    FROM "suser_customuser"
    WHERE "suser_customuser"."id" < 10)) U0
 group by is_active, id
 }}}


 i think this is bug, if not why not show any warning or exception?
 or just say how rewrite query for correct use Subquery

 screenshot:
 http://dl4.joxi.net/drive/2019/02/24/0002/0003/143363/63/2eab4a5318.jpg

-- 
Ticket URL: <https://code.djangoproject.com/ticket/30209>
Django <https://code.djangoproject.com/>
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