#33768: MySQL ordering of nulls last/first is broken in combination with UNION
-------------------------------------+-------------------------------------
Reporter: Florian Apolloner | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: dev
(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
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Changes (by Simon Charette):
* cc: Simon Charette (added)
Comment:
What if we performed a subquery pushdown instead to make compilation more
predictable so we can have the order by clause refer to the union columns
by name?
{{{#!sql
SELECT `other_num`
FROM (
(SELECT `queries_number`.`other_num` FROM `queries_number` WHERE
`queries_number`.`num` <= 1)
UNION
(SELECT `queries_number`.`other_num` FROM `queries_number` WHERE
`queries_number`.`num` >= 2)
)
ORDER BY `other_num` IS NULL
}}}
This is a strategy that is used successfully for aggregation for example.
I don't see `OrderBy.as_sql` usage of `template` for compilation is an
abuse at all; it's in charge of it's own compilation unit. As mentioned on
#33767 I'd prefer if we errored out on constant order by usage instead of
making leaps to support it because it has ambiguous evaluation rules.
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Ticket URL: <https://code.djangoproject.com/ticket/33768#comment:2>
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