ST_Union
Signatures
GEOMETRY ST_Union(GEOMETRY geomA);
GEOMETRY ST_Union(GEOMETRY geomA, GEOMETRY geomB);
GEOMETRY ST_Union(GEOMETRYCOLLECTION geom);
Description
ST_Union can be used as a scalar or an aggregate function.
Scalar function
Computes the union of one or more Geometries.
Input Geometries can be (MULTI)POINTs, (MULTI)LINESTRINGs, (MULTI)POLYGONs or GEOMETRYCOLLECTIONs.
Aggregate function
Computes the union of a set of Geometries.
geom is a GEOMETRYCOLLECTION resulting from an ST_Accum operation on a table.
In both cases:
If no input Geometriy is given, the result is
NULL.Output Geometries can be single or multiple.
Note
Implements the OpenGIS Simple Features Implementation Specification for SQL version 1.2.1
Examples
Scalar function
geomA Polygon |
geomB Polygon |
|---|---|
POLYGON((1 1, 7 1, 7 6, 1 6, 1 1)) |
POLYGON((3 2, 8 2, 8 8, 3 8, 3 2)) |
SELECT ST_Union(geomA, geomB) FROM input_table;
-- Answer: POLYGON((7 2, 7 1, 1 1, 1 6, 3 6, 3 8, 8 8, 8 2, 7 2))
Aggregate function
CREATE TABLE input_table(geom GEOMETRY(POLYGON));
INSERT INTO input_table VALUES
('POLYGON((1 1, 7 1, 7 6, 1 6, 1 1))'),
('POLYGON((3 2, 8 2, 8 8, 3 8, 3 2))'),
('POLYGON((1 7, 2 7, 2 8, 1 8, 1 7))');
SELECT ST_Union(ST_Accum(geom)) FROM input_table;
-- Answer: MULTIPOLYGON(((7 2, 7 1, 1 1, 1 6, 3 6, 3 8, 8 8, 8 2, 7 2)),
-- ((1 7, 2 7, 2 8, 1 8, 1 7)))
