ST_NumGeometries function to return the number of geometry objects - ApsaraDB RDS

Returns the number of geometry objects in a geometry collection. For a single geometry object, returns 1. For all other input, returns NULL.

Syntax

integer ST_NumGeometries(geometry geom);

Parameter	Description
geom	The geometry object. Supported types include geometry collections (GeometryCollection, MULTI objects), single geometry objects, polyhedral surfaces, triangles, triangulated irregular network (TIN) surfaces, and 3D objects.

Query the number of geometries in a MULTIPOLYGON:

SELECT ST_NumGeometries('MULTIPOLYGON(((1 0,0 3,3 0,1 0)),((1 0,2 0,0 2,1 0)))'::geometry);

Output:

 st_numgeometries
------------------
                2
(1 row)

Query the number of geometries in a GeometryCollection:

SELECT ST_NumGeometries('GeometryCollection(POINT(1 0),POLYGON((1 0,2 0, 0 2,1 0)))'::geometry);

Output:

 st_numgeometries
------------------
                2
(1 row)