[Django] #32200: Aggregating when grouping on an ExpressionWrapper omits the expression from the group by

[Django]

#32200: Aggregating when grouping on an ExpressionWrapper omits the expression 
from
the group by
------------------------------------------+------------------------
               Reporter:  Gordon Wrigley  |          Owner:  nobody
                   Type:  Uncategorized   |         Status:  new
              Component:  Uncategorized   |        Version:  3.1
               Severity:  Normal          |       Keywords:
           Triage Stage:  Unreviewed      |      Has patch:  0
    Needs documentation:  0               |    Needs tests:  0
Patch needs improvement:  0               |  Easy pickings:  0
                  UI/UX:  0               |
------------------------------------------+------------------------
 I ran into this with Postgres on Django 3.1.3, I'm not sure what other
 versions it exists on.

 {{{
 #!python
 print(
     Fred.objects.annotate(
         bob_id__is_null=ExpressionWrapper(
             Q(bob_id=None),
             output_field=BooleanField()
         )
     ).values(
         "bob_id__is_null"
     ).annotate(
         id__count=Count("id", distinct=True)
     ).values(
         "bob_id__is_null",
         "id__count"
     ).query
 )
 }}}

 {{{
 #!sql
 SELECT
     "main_fred"."bob_id" IS NULL AS "bob_id__is_null",
     COUNT(DISTINCT "main_fred"."id") AS "id__count"
 FROM "main_fred"
 GROUP BY "main_fred"."bob_id"
 }}}

 On the last line there the group by has dropped the "IS NULL"

-- 
Ticket URL: <https://code.djangoproject.com/ticket/32200>
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