14.16.7.5 GeometryCollection Property Functions

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 is NULL.

• 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:

• ST_GeometryN(gc, N)

  Returns the N-th geometry in the GeometryCollection value gc. 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)                                      |
  +-------------------------------------------------+

• ST_NumGeometries(gc)

  Returns the number of geometries in the GeometryCollection value gc.

  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 |
  +----------------------------------------+