Name
ST_MemUnion — Same as ST_Union (aggregate) but memory-friendly (uses less memory and more processor time).
Synopsis
PostgreSQL
geometry ST_MemUnion(bytea
GeometryAggregate);
H2
geometry ST_MemUnionAgg(bytea
GeometryAggregate);
Description
Same as ST_Union (aggregate) but memory-friendly (uses less memory and more processor time). It works by unioning the geometries one at a time to previous result as opposed to ST_Union aggregate which first creates an array and then unions
Coordinate Dimensions
| 2D | 3D | M |
|---|---|---|
 | | |
Spatial Standards Support
| OGC SFS for SQL. 1.1 (1999) | OGC SFS for SQL. 1.1.0 (2005) | OGC SFS for SQL. 1.2.0 (2006) | SQL-MM Part 3 |
|---|---|---|---|
| - | - | - | - |
Examples
CREATE TABLE "polygons"(id serial PRIMARY KEY);
SELECT AddGeometryColumn ('polygons','GEOM',25830,'POLYGON',2);
INSERT INTO "polygons" ("GEOM") VALUES (ST_GeomfromEWKT('SRID=25830;POLYGON ((40 20 10, 40 100 15, 120 100 25, 120 20 30, 40 20 25))'));
INSERT INTO "polygons" ("GEOM") VALUES (ST_GeomfromEWKT('SRID=25830;POLYGON ((80 60, 80 130, 170 130, 170 60, 80 60))'));
--PostgreSQL
SELECT asewkt(ST_MemUnion("polygons"."GEOM")) as union_pol from "polygons";
--H2
SELECT asewkt(ST_MemUnionAgg("polygons"."GEOM")) as union_pol from "polygons";
SELECT DropGeometryTable ('polygons');
--Result
UNION_POL
SRID=25830;POLYGON ((40 20 10, 40 100 15, 80 100 0, 80 130 0, 170 130 0, 170 60 0, 120 60 0, 120 20 30, 40 20 25))