ST_Difference( ST_Geometry ) method

Returns the geometry value that represents the point set difference of two geometries.

Syntax

geometry-expression.ST_Difference( ST_Geometry geo2)

geo2 – The other geometry value that is to be subtracted from the geometry-expression.

ST_Geometry Returns the geometry value that represents the point set difference of two geometries.

Example 1 – The following example shows the difference (C) of a square (A) with a circle (B) removed and the difference (D) of a circle (B) with a square (A) removed.
```
SELECT NEW ST_Polygon( 'Polygon( (-1 -0.25, 1 -0.25, 1 2.25, -1 2.25, -1 -0.25) )' ) AS A
, NEW ST_CurvePolygon( 'CurvePolygon( CircularString( 0 1, 1 2, 2 1, 1 0, 0 1 ) )' )  AS B
, A.ST_Difference( B ) AS C
, B.ST_Difference( A ) AS D
```
The following picture shows the difference C=A-B and D=B-A as the shaded portion of the picture. Each difference is a single surface that contains all of the points that are in the geometry on the left hand side of the difference and not in the geometry on the right hand side. Union of a square and a circle

SQL/MM (ISO/IEC 13249-3: 2006) 5.1.20