Paragon Corporation wrote:
All RDBMS I know when you sum up things with nulls you get the result
without the null (there are rare aggregates where it is not advantageous to
do that). Whether that is right or wrong is another question, but it seems
pretty baked into the standard
of how RDBMS work and its convenient because in general that's the behavior
you want and its easy to generate the reverse behavior of what you describe
by slapping a coalesce/case when everywhere, but its not quite so easy to go
the other way around. Think about it how would you say count only things
that aren't null.
It seems wise not to buck the trend in this instance; it seems that the
commonly expected behaviour is for aggregates to ignore null inputs, but
return null only if the input set is empty.
Charlie, if you want to experiment with this AFAICT the fix is simple:
remove the STRICT declaration from ST_unite_garray in lwpostgis.sql.
This should then allow the aggregate to continue if a null is encountered.
Oh and again, please file on the PostGIS bug tracker lest we forget :)
Is an empty geometry value different from a null in a geometry column?
Can an empty geometry have a SRID (& a null can't)?
In what cases would it make sense to replace null geometries with empty
ones?
No. They are not functionally the same. For example the intersection of 2
disjoint geometries is obviously an empty collection - it is known therefore
it is not null
And that empty collection should have the same srid of the 2 geometries
being intersected.
I think the question being asked here is: does an empty
geometrycollection have a SRID? My instinct says no, but then I don't
deal with them enough everyday to get a feeling for what the expected
behaviour should be.
ATB,
Mark.
--
Mark Cave-Ayland
Sirius Corporation - The Open Source Experts
http://www.siriusit.co.uk
T: +44 870 608 0063
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