[postgis-users] Union as an aggregate

[David Blasby]

strk wrote:
> Dave, I made no special 'unite' code, just sql create command:
> CREATE AGGREGATE unite (
> 	sfunc = GeomUnion,
> 	basetype = geometry,
> 	stype = geometry
> );

Hum - this shouldnt do anything.

The aggregate should have "null" as its initial value.

GeomUnion(null,<geometry>) --> null.

So, you'll end up with null *very* quickly because 
GeomUnion(null,<geometry>) returns null without any actual execution.


Are you running this on a big table?  At worst I'd expect this to use up 
memory the same size all the geometries in the table.

I'll look more at this tomorrow.


dave

ps. just as a test, try redefining your unite to:
  CREATE AGGREGATE unite (
  	sfunc = GeomUnion,
  	basetype = geometry,
  	stype = geometry,
         initial_condition = '<wkt>'
  );
Where <wkt> is the well known text of one of the geometries in your 
table.  This will force the initial function to be:

GeomUnion(<wkt>,<geometry>) --> <geometry>

And things might work.  If this does work, then the problem is that the 
postgresql aggregate function code isnt paying attention to the 
"isstrict" tags on the base ("geomUnion") function.