ST_NumGeometries function

The ST_NumGeometries function takes a geometry collection as an input parameter and returns the number of geometries in the collection.

If the specified geometry collection is null or is empty, then null is returned.

Syntax

Parameter

collection: A value of type ST_GeomCollection or one of its subtypes that represents the geometry collection for which the number of geometries is returned.

Return Type

INTEGER

Example

Two geometry collections are stored in the SAMPLE_GEOMCOLL table. One is a multipolygon, and the other is a multipoint. The ST_NumGeometries function determines how many individual geometries are within each geometry collection.


CREATE TABLE sample_geomcoll (id INTEGER, geometry ST_GeomCollection)

INSERT INTO sample_geomcoll
  VALUES (1,
          ST_MultiPolygon ('multipolygon (( (3 3, 4 6, 5 3, 3 3),
                                (8 24, 9 25, 1 28, 8 24),
                                (13 33, 7 36, 1 40, 10 43, 13 33) ))', 1) )

INSERT INTO sample_geomcoll
  VALUES (2, ST_MultiPoint ('multipoint (1 2, 4 3, 5 6, 7 6, 8 8)', 1) )

SELECT id, ST_NumGeometries (geometry) NUM_GEOMS_IN_COLL
  FROM sample_geomcoll

Results:


ID          NUM_GEOMS_IN_COLL
----------- -----------------
          1                 3
          2                 5