[postgis-users] st_union returning null on various (valid) sets of polygons/multipolygons

[Andrea Peri 2007]

Hi,

I try

select
    1 as id,
    st_union(a.geom) as geom
from
    public._postgis_selezione_ok as a
;

It seem work pretty fast and result seem ok.

Andrea.


>I'm trying to apply ST_Union on a set of geometries (multypolygons,
>most of which containing a single geometry), to test the CascadedUnion
>performance, but the most of times it returns a null result. I haven't
>been able to find a rule: sometimes it seems to be the number of
>geometries, sometimes the order, etc.
>Could someone replicate it? Here is a small selection of my layer (it
>contains already validated geometries):
>http://www.giovanniallegri.it/share/postgis_selection.zip
>
>thanks a lot,
>
>Giovanni