These functions return properties of
GeometryCollection
values.
Unless otherwise specified, functions in this section handle their geometry arguments as follows:
If any argument is
NULL
or any geometry argument is an empty geometry, the return value isNULL
.If any geometry argument is not a syntactically well-formed geometry, an
ER_GIS_INVALID_DATA
error occurs.If any geometry argument is a syntactically well-formed geometry in an undefined spatial reference system (SRS), an
ER_SRS_NOT_FOUND
error occurs.Otherwise, the return value is non-
NULL
.
These functions are available for obtaining geometry collection properties:
Returns the
N
-th geometry in theGeometryCollection
valuegc
. Geometries are numbered beginning with 1.ST_GeometryN()
handles its arguments as described in the introduction to this section.mysql> SET @gc = 'GeometryCollection(Point(1 1),LineString(2 2, 3 3))'; mysql> SELECT ST_AsText(ST_GeometryN(ST_GeomFromText(@gc),1)); +-------------------------------------------------+ | ST_AsText(ST_GeometryN(ST_GeomFromText(@gc),1)) | +-------------------------------------------------+ | POINT(1 1) | +-------------------------------------------------+
Returns the number of geometries in the
GeometryCollection
valuegc
.ST_NumGeometries()
handles its arguments as described in the introduction to this section.mysql> SET @gc = 'GeometryCollection(Point(1 1),LineString(2 2, 3 3))'; mysql> SELECT ST_NumGeometries(ST_GeomFromText(@gc)); +----------------------------------------+ | ST_NumGeometries(ST_GeomFromText(@gc)) | +----------------------------------------+ | 2 | +----------------------------------------+