#26067: Orderable ArrayAgg and StringAgg
---------------------------------+-----------------------------------------
Reporter: fdh | Owner:
Type: New feature | Status: new
Component: | Version:
contrib.postgres |
Severity: Normal | Keywords: ArrayAgg StringAgg ordering
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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The [http://www.postgresql.org/docs/9.0/static/functions-aggregate.html
documentation] of Postgres 9.0 first mentions the possibility of ordering
the results within aggregations such as ARRAY_AGG and STRING_AGG.
This could be useful in some cases.
For example: it could make sense to perform a StringAgg in lexicographical
order in some cases.
The basic format of ordering within aggregations in SQL is quite simple:
{{{
#!sql
SELECT ARRAY_AGG(some_field ORDER BY some_field ASC) FROM table;
SELECT ARRAY_AGG(some_field ORDER BY some_field DESC) FROM table;
SELECT ARRAY_AGG(some_field ORDER BY other_field ASC) FROM table;
}}}
It would be nice if the above would be supported as follows:
{{{
#!python
Model.objects.aggregate(ArrayAgg(some_field, order_by='some_field'))
Model.objects.aggregate(ArrayAgg(some_field, order_by='-some_field'))
Model.objects.aggregate(ArrayAgg(some_field, order_by='other_field'))
}}}
where order_by is an optional parameter. If it not specified, behavior can
remain unchanged from the current implementation.
As noted by Josh Smeaton in the [https://groups.google.com/forum/#!topic
/django-developers/YCSDX3GApBM mailinglist] discussion for this feature,
any ordering added within '''may''' need to be contributed to GROUP BY.
This might require some investigation.
--
Ticket URL: <https://code.djangoproject.com/ticket/26067>
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