union function
Returns a geometry that represents the point set union of the geometries.
Syntax
union( a, b )
Arguments
a → geometry
b → geometry
Example
geomToWKT( union( geomFromWKT( 'POINT(4 4)' ) , geomFromWKT( 'POINT(5 5)' )) ) → returns MULTIPOINT(4 4, 5 5)