GROUP BY on a table with geometry

Question

Good evening
This is an overview of my table
Geometry_|_ID_GEO_|_Year_|_Value
Polygon1_|__1______|_1999_|__5
Polygon1_|__1______|_1999_|__7
Polygon2_|__2______|_1999_|__4
Polygon2_|__2______|_1999_|__12
I would like to group this table by geometry and by year suming the value to obtain something like that:
Geometry_|_ID_GEO_|_Year_|_Value
Polygon1_|__1______|_1999_|__12
Polygon2_|__2______|_1999_|__16
I have written the following SQL statement which work perfectly:
SELECT SUM(Value),ID_GEO FROM MyTable WHERE Year=1999 GROUP BY ID_GEO
But when i add the Geometry field in the statement like:
SELECT Geometry,SUM(Value),ID_GEO FROM MyTable WHERE Year=1999 GROUP BY ID_GEO
It does not work anymore. I obtain an error: SQLState: 42000, ErrorCode: 979 which seems to be related to the Group by...
The point is that i need the Geometry in the result query to then generate a map.
I am using Oracle entreprise 10 with oracle Locator only.
Can anyone help me? I don't understand why it does not work.
Many thanks
Sylvain

Answer 1

I was faced with a similar issue more than a year ago. The solution for me was to create an user defined aggregate function: agg_first_geom. This will help aggragating your data by keeping/taking the first geometry. This of course is valid when you have a 1 to 1 relationship with one of the columns in your group by, which you confirmed earlier.
Try it and see whether this could be of help.
first create the type agg_geom_t and the function agg_first_geom. Once that is finished you should be able to have your SQL statement as follows:
SELECT SUM(Value) as SUMOfValue ,ID_GEO, agg_first_geom(geometry) FROM MyTable WHERE Year=1999 GROUP BY ID_GEO
create or replace type agg_geom_t as object (
    geom_agg mdsys.sdo_geometry,
    static function ODCIAggregateInitialize(sctx in out agg_geom_t)
        return number,
    member function ODCIAggregateIterate(self in out agg_geom_t,
        value in mdsys.sdo_geometry) return number,
    member function ODCIAggregateTerminate(self in agg_geom_t,
        return_value out mdsys.sdo_geometry, flags in number) return number,
    member function ODCIAggregateMerge(self in out agg_geom_t,
        ctx2 in agg_geom_t) return number
create or replace type body agg_geom_t is
    static function ODCIAggregateInitialize(sctx in out agg_geom_t)
        return number is
    begin
        sctx := agg_geom_t(null);
        return ODCIConst.Success;
    end;
    member function ODCIAggregateIterate(
      self in out agg_geom_t, value in mdsys.sdo_geometry)
        return number is
    begin
        geom_agg := value;
        return ODCIConst.Success;
    end;
    member function ODCIAggregateTerminate(self in agg_geom_t,
        return_value out mdsys.sdo_geometry, flags in number) return number is
    begin
        return_value := geom_agg;
        return ODCIConst.Success;
    end;
    member function ODCIAggregateMerge(self in out agg_geom_t,
        ctx2 in agg_geom_t) return number is
    begin
     geom_agg := ctx2.geom_agg;
        return ODCIConst.Success;
    end;
end;
create or replace function agg_first_geom (input mdsys.sdo_geometry) return mdsys.sdo_geometry
    parallel_enable aggregate using agg_geom_t;
commit;SELECT SUM(Value) as SUMOfValue ,ID_GEO, agg_first_geom(geometry) FROM MyTable WHERE Year=1999 GROUP BY ID_GEO