#30130: Django .values().distinct() returns a lot more records than
.values().distinct().count()
-------------------------------------+-------------------------------------
Reporter: James Lin | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 2.1
(models, ORM) |
Severity: Normal | Resolution:
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 Simon Charette):
I'm pretty sure that's what's at play here as I managed to reproduce
locally. You have a defined `Meta.ordering` (or are performing an
`order_by`) which makes your non-count query something along the lines of
{{{#!sql
SELECT DISTINCT "machine", "cluster", "ordering" FROM "resources" ORDER BY
"ordering" ASC
}}}
The `ordering` column is added to the `SELECT` clause to prevent the
generation of invalid SQL.
{{{#!sql
SELECT DISTINCT "machine", "cluster" FROM "resources" ORDER BY "ordering"
ASC
> ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select
list
}}}
The `.count()` query happens to be the following
{{{#!sql
SELECT COUNT(*) FROM (SELECT DISTINCT "ticket_30130_foo"."bat" AS Col1,
"ticket_30130_foo"."baz" AS Col2 FROM "ticket_30130_foo") subquery
}}}
It looks like the issue is that
[https://github.com/django/django/blob/7e978fdc4228eb44cf97cb4243adc7b7bfd586c7/django/db/models/sql/query.py#L439-L443
we clear the ordering when we shouldn't] on the `.count()`. I think the
logic needs to be adjusted to branch of `not self.distinct` instead of
`self.distinct_fields`.
--
Ticket URL: <https://code.djangoproject.com/ticket/30130#comment:4>
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