#30685: Suboptimal QuerySet.distinct().count()
-------------------------------------+-------------------------------------
     Reporter:  Adam Sołtysik        |                    Owner:  nobody
         Type:                       |                   Status:  new
  Cleanup/optimization               |
    Component:  Database layer       |                  Version:  2.2
  (models, ORM)                      |
     Severity:  Normal               |               Resolution:
     Keywords:                       |             Triage Stage:  Accepted
    Has patch:  0                    |      Needs documentation:  0
  Needs tests:  0                    |  Patch needs improvement:  0
Easy pickings:  0                    |                    UI/UX:  0
-------------------------------------+-------------------------------------

Comment (by Adam Sołtysik):

 Thank you for accepting. I have added `.values('pk').order_by()` before my
 `.count()` queries, but I'll be glad to be able to get rid of it.

 Just to add a bit more information. The "problem" is not only with
 `.distinct()`, also any `.annotate()` makes `count()` produce a subquery
 with the redundant annotations inside. For example, a query like this
 results in SQL that is 4 times slower for my data than the bare count:

 {{{Model.objects.annotate(id2=F('id')).count()}}}
 {{{(0.057) SELECT COUNT(*) FROM (SELECT "table"."id" AS Col1, "table"."id"
 AS "id2" FROM "table" GROUP BY "table"."id") subquery;}}}

 Adding `.values('pk')` of course solves this as well.

-- 
Ticket URL: <https://code.djangoproject.com/ticket/30685#comment:6>
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