Description

Returns a geometry that represents the portions of A and B that do not intersect. It is called a symmetric difference because ST_SymDifference(A,B) = ST_SymDifference(B,A). One can think of this as ST_Union(geomA,geomB) - ST_Intersection(A,B).

Performed by the GEOS module

This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.3

This method implements the SQL/MM specification. SQL-MM 3: 5.1.21

This function supports 3d and will not drop the z-index. However it seems to only consider x y when doing the difference and tacks back on the Z-Index

Examples

The original linestrings shown together

The symmetric difference of the two linestrings

--Safe for 2d - symmetric difference of 2 linestrings
SELECT ST_AsText(
	ST_SymDifference(
		ST_GeomFromText('LINESTRING(50 100, 50 200)'),
		ST_GeomFromText('LINESTRING(50 50, 50 150)')
	)
);

st_astext
---------
MULTILINESTRING((50 150,50 200),(50 50,50 100))

--When used in 3d doesn't quite do the right thing
SELECT ST_AsEWKT(ST_SymDifference(ST_GeomFromEWKT('LINESTRING(1 2 1, 1 4 2)'),
	ST_GeomFromEWKT('LINESTRING(1 1 3, 1 3 4)')))

st_astext
------------
MULTILINESTRING((1 3 2.75,1 4 2),(1 1 3,1 2 2.25))
		

See Also

ST_Difference, ST_Intersection, ST_Union