18.5.3.2. Spatial Operators
OpenGIS proposes a number of other functions that can produce
geometries. They are designed to implement spatial operators.
These functions are not implemented in MySQL. They may appear
in future releases.

Buffer(g
,d
)
Returns a geometry that represents all points whose
distance from the geometry value
g
is less than or equal to a
distance of d
.

ConvexHull(g
)
Returns a geometry that represents the convex hull of the
geometry value g
.

Difference(g1
,g2
)
Returns a geometry that represents the point set
difference of the geometry value
g1
with
g2
.

Intersection(g1
,g2
)
Returns a geometry that represents the point set
intersection of the geometry values
g1
with
g2
.

SymDifference(g1
,g2
)
Returns a geometry that represents the point set symmetric
difference of the geometry value
g1
with
g2
.

Union(g1
,g2
)
Returns a geometry that represents the point set union of
the geometry values g1
and
g2
.