ST_Union

Calculates the union of all points in two spatial objects.

This result is represented mathematically by: g1 È g2

Behavior Type

Immutable

Syntax

ST_Union( g1, g2 )

Arguments

g1

Spatial object, type GEOMETRY

g2

Spatial object, type GEOMETRY

Returns

GEOMETRY

Supported Data Types

Data Type GEOMETRY
Point

Yes

Multipoint

Yes

Linestring

Yes

Multilinestring

Yes

Polygon

Yes

Multipolygon

Yes

GeometryCollection

Yes

Example

The following example shows how to use ST_Union.

Returns a polygon that represents all the points contained in these two polygons:

 

=> SELECT ST_AsText(ST_Union(ST_GeomFromText('POLYGON((0 2,1 1,0 -1,-1 1,0 2))'),
   ST_GeomFromText('POLYGON((-1 2, 0 0, -2 0, -1 2))')));
                                     ST_AsText                                      
------------------------------------------------------------------------------
 POLYGON ((0 2, 1 1, 0 -1, -0.5 0, -2 0, -1 2, -0.666666666667 1.33333333333, 0 2))
(1 row)