#30685: Suboptimal QuerySet.distinct().count()
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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
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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.
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Ticket URL: <https://code.djangoproject.com/ticket/30685#comment:6>
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