#26067: Orderable ArrayAgg and StringAgg
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Reporter: fdh | Owner: fdh
Type: New feature | Status: assigned
Component: contrib.postgres | Version: master
Severity: Normal | Resolution:
Keywords: ArrayAgg StringAgg | Triage Stage: Accepted
ordering |
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 fdh):
As pointed out by Josh Smeaton in the mailing list
[https://groups.google.com/forum/#!topic/django-developers/YCSDX3GApBM
discussion]:
Consider that any ordering added within *may* need to be contributed to
GROUP BY, but I haven't read the documentation to say that is a
requirement.
In the Postgres' [https://www.postgresql.org/docs/9.5/static/functions-
aggregate.html documentation] these aggregations are only mentioned as
being special by meaningful difference in ordering input values:
The aggregate functions array_agg, [...] string_agg, and xmlagg, as well
as similar user-defined aggregate functions, produce meaningfully
different result values depending on the order of the input values. This
ordering is unspecified by default, but can be controlled by writing an
ORDER BY clause within the aggregate call, as shown in Section 4.2.7.
I don't think anything in the ORDER BY clause in the aggregation would
have to be contributed to a GROUP BY clause in the surrounding query as
the aggregation operation is independent of the grouping of the
surrounding query.
--
Ticket URL: <https://code.djangoproject.com/ticket/26067#comment:4>
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