ST_Union

ST_Union returns a geometry representing the union of two geometries. That is, it merges the input geometries to produce a resulting geometry with no overlaps.

Syntax

ST_Union(geom1, geom2)

Arguments

geom1

A value of data type GEOMETRY or an expression that evaluates to a GEOMETRY type.

geom2

A value of data type GEOMETRY or an expression that evaluates to a GEOMETRY type.

Return type

GEOMETRY

The spatial reference system identifier (SRID) value of the returned geometry is the SRID value of the input geometries.

If geom1 or geom2 is null, then null is returned.

If geom1 or geom2 are empty, then an empty geometry is returned.

If geom1 and geom2 don't have the same value for the spatial reference system identifier (SRID), then an error is returned.

If geom1 or geom2 is a geometry collection, linestring, or multilinestring, then an error is returned.

If geom1 or geom2 is not a two-dimensional (2D) geometry, then an error is returned.

Examples

The following SQL returns the non-empty geometry representing the union of two input geometries.

SELECT ST_AsEWKT(ST_Union(ST_GeomFromText('POLYGON((0 0,100 100,0 200,0 0))'), ST_GeomFromText('POLYGON((0 0,10 0,0 10,0 0))')));

        st_asewkt        
-------------------------
 POLYGON((0 0,0 200,100 100,5 5,10 0,0 0))