#30685: Suboptimal QuerySet.distinct().count()
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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
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Comment (by Carlton Gibson):
I think the issue is that there's no way for the `distinct()` call to know
that you're going to follow up with a `count()` — and that code to special
case for that isn't going to worth the effort.
If you know you only want to select a single field tell the ORM via
[https://docs.djangoproject.com/en/2.2/ref/models/querysets/#django.db.models.query.QuerySet.only
`only()`]. This'll give you want you need, I think:
`Model.objects.only('id').distinct().count()`.
(Maybe the ORM experts can tell you more, but I suspect that be more or
less the end of the story...)
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Ticket URL: <https://code.djangoproject.com/ticket/30685#comment:3>
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