Amazon Redshift will no longer support the use of Python UDFs after June 30, 2026. We will start enforcing it in phases. For more information on the details of Python end of life and migration options, see the blog post that was published on June 30, 2025.

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

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))