#36875: Avoid unnecessary Coalesce in Concat/ConcatPair
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Reporter: David | Owner: Rusheel
Type: | Chandra Reddy
Cleanup/optimization | Status: assigned
Component: Database layer | Version: 5.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: concat,coalese | 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 Simon Charette):
Before making any changes here we should consider the context from #25517,
#29582, #30385, #34955.
> if any involved expression have nullable output (which I understand can
be hard to check)
This is particularly relevant as the ORM doesn't do a good job at
differentiaing nullable expression, we can't use `expr.output_field.null`
as we don't update this flag transitively when performing outer joins.
That's the main reason why we systematically `Coalesce` each expression.
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Ticket URL: <https://code.djangoproject.com/ticket/36875#comment:3>
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