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

Comment (by adamsol):

 I don't think it's a bug, but I think there is a place for optimization. I
 can't see a reason why all columns are SELECTed in a subquery just to
 perform a simple count. I've attached the SQLs generated and what I would

 So, for any model, a query like this:


 should produce an SQL like this:

 "table") subquery;}}}

 instead of:

 {{{SELECT COUNT(*) FROM (SELECT DISTINCT "table"."id" AS Col1, ... (all
 other columns) FROM "table") subquery;}}}

 which, depending on the number of columns and size of the table, can be
 several times slower (at least on PostgreSQL).

 If you think this is not worth the effort, then OK, I won't insist.

Ticket URL: <https://code.djangoproject.com/ticket/30685#comment:2>
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