# ST_SymDifference function

The ST_SymDifference function takes two geometries as input parameters and returns the geometry that is the symmetrical difference of the two geometries. The symmetrical difference is the non-intersecting part of the two specified geometries.

The resulting geometry is represented in the spatial reference system of the first geometry. The dimension of the returned geometry is the same as that of the input geometries. Both geometries must be of the same dimension.

If the second geometry is not represented in the same spatial reference system as the first geometry and uses the same underlying datum, it will be converted to the other spatial reference system.

If the geometries are equal, an empty geometry of type ST_Point is returned. If either geometry is null, then null is returned.

The resulting geometry is represented in the most appropriate spatial type. If it can be represented as a point, linestring, or polygon, then one of those types is used. Otherwise, the multipoint, multilinestring, or multipolygon type is used.

## Parameters

geometry1
A value of type ST_Geometry or one of its subtypes that represents the first geometry to compute the symmetrical difference with geometry2.
geometry2
A value of type ST_Geometry or one of its subtypes that represents the second geometry to compute the symmetrical difference with geometry1.

ST_Geometry

## Examples

Example 1
This example illustrates the use of the ST_SymDifference function. The geometries are stored in the SAMPLE_GEOMS table.
``````
CREATE TABLE sample_geoms (id INTEGER, geometry ST_Geometry)

INSERT INTO sample_geoms
VALUES
(1, ST_Geometry('polygon((10 10,10 20,20 20,20 10,10 10))',0))

INSERT INTO sample_geoms
VALUES
(2, ST_Geometry('polygon((30 30,30 50,50 50,50 30,30 30))',0))

INSERT INTO sample_geoms
VALUES
(3, ST_Geometry('polygon((40 40,40 60,60 60,60 40,40 40))',0))

INSERT INTO sample_geoms
VALUES
(4, ST_Geometry('linestring(70 70, 80 80)',0))

INSERT INTO sample_geoms
VALUES
(5,ST_Geometry('linestring(75 75,90 90)',0));
``````
In the following examples, the results have been reformatted for readability. Your results will vary according to your display.
Example 2
This example uses ST_SymDifference to return the symmetric difference of two disjoint polygons in the SAMPLE_GEOMS table.
``````
SELECT a.id as id1, b.id as id2,
CAST (ST_AsText (ST_SymDifference (a.geometry, b.geometry) )
AS VARCHAR(350) ) SYM_DIFF
FROM sample_geoms a, sample_geoms b
WHERE a.id = 1 AND b.id = 2
``````
Results:
``````
ID1 ID2 SYM_DIFF
--- --- -------------------------------------------------------------------
1   2 MULTIPOLYGON (((10 10, 20 10, 20 20, 10 20, 10 10)),
((30 30, 50 30, 50 50, 30 50, 30 30)))
``````
Example 3
This example uses ST_SymDifference to return the symmetric difference of two intersecting polygons in the SAMPLE_GEOMS table.
``````
SELECT a.id as id1, b.id as id2,
CAST (ST_AsText (ST_SymDifference (a.geometry, b.geometry) )
AS VARCHAR(500) ) SYM_DIFF
FROM sample_geoms a, sample_geoms b
WHERE a.id = 2 AND b.id = 3
``````
Results:
``````
ID1 ID2 SYM_DIFF
--- --- -------------------------------------------------------------------
2   3 MULTIPOLYGON (((40 50, 50 50, 50 40, 60 40, 60 60, 40 60, 40 50)),
((30 30, 50 30, 50 40, 40 40, 40 50, 30 50, 30 30)))
``````
Example 4
This example uses ST_SymDifference to return the symmetric difference of two intersecting linestrings in the SAMPLE_GEOMS table.
``````
SELECT a.id as id1, b.id as id2,
CAST (ST_AsText (ST_SymDifference (a.geometry, b.geometry) )
AS VARCHAR(350) ) SYM_DIFF
FROM sample_geoms a, sample_geoms b
WHERE a.id = 4 AND b.id = 5
``````
Results:
``````
ID1 ID2 SYM_DIFF
--- --- ---------------------------------------------------------------------
4   5 MULTILINESTRING ((70 70, 75 75),(80 80, 90 90))

``````