[postgis-users] GeometryCollection(Empty) is SRID dependent (orsupporting nulls in st_union)

[Charlie Savage]

> 
> "... the aggregate functions (SUM, AVG, etc) ... simply egnore any nulls
> in their argument (except for COUNT(*)) ... if the argument to such a
> function happens to evaluate to an empty set, the functions all return
> null (except for COUNT, which returns zero."
> 
> This from page 222-3,_A Guide to the SQL Standard_, Third Edition, Date
> C.J. and Hugh Darwen, 1993 Addison Wesley.


So - do we have agreement that NULL's should be ignored in functions 
that act on aggregates?

To recap:

* NULL values cause functions such as ST_UNION to return NULL
* This is counter to postgresql's built in aggregates, such as 
avg/max/min, which ignore the NULL values


I think PostGis should change to match the postgresql semantics.

Charlie
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