Re: Wrong result of <select distinct geometry from XXX>

On Tue, Apr 5, 2016 at 11:04 PM, yuanrui <yuanrui(at)pset(dot)suntec(dot)net> wrote:
>
> Sorry to bother.
> I have encountered the following problem, please help me.
>
> The attached file is a backup file of two geometries, the table name is
> <temp_union_test>, the column of geometry is <the_geom>.
> when I execute < select distinct the_geom from temp_union_test >, there is
> only one row returned, but actually, the two geometries is totally
> different.

I think this might have something to do with weird legacy issues that
PostGIS has:

http://www.postgresql.org/message-id/etPan.559d8d4b.7c83e458.e975@Crane.local

This is basically a mistake that PostGIS made, but is now stuck with.

What does EXPLAIN show the plan as? Do you get a difference answer
when the plan is a hashAggregate instead of a unique + sort? You can
test this using "set enable_hashagg = off", or maybe "set enable_sort
= off" depending on the details (could be an index scan instead of a
sort for a unique node).

--
Peter Geoghegan