[postgis-devel] ST_Union, ST_Collect and ST_Difference strictness

[Darafei "Komяpa" Praliaskouski]

>
>
> NULL is for "unknown", while what you're after is an EMPTY
> How about seeing if ST_Union(geom) can return an EMPTY when passed
> nothing ?
>

For EMPTY that is made from ST_Union of zero rows, you don't have a SRID.
You can in theory allow operations between an empty of different SRID, but
you cannot store it a column that has a SRID.

I think both proposals are good in terms of user experience, but as long as
SRID is part of geometry body, but not header, your does not seem simple to
implement.
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