ST_NRings

ST_NRings returns the number of rings in an input geometry.

Syntax

ST_NRings(geom)

Arguments

geom

A value of data type GEOMETRY or an expression that evaluates to a GEOMETRY type.

Return type

INTEGER

If geom is null, then null is returned.

The values returned are as follows.

Returned value	Geometry subtype
0	Returned if geom is a POINT, LINESTRING, MULTIPOINT, or MULTILINESTRING subtype
The number of rings.	Returned if geom is a POLYGON or MULTIPOLYGON subtype
The number of rings in all components	Returned if geom is a GEOMETRYCOLLECTION subtype

Examples

The following SQL returns the number of rings in a multipolygon.

SELECT ST_NRings(ST_GeomFromText('MULTIPOLYGON(((0 0,10 0,0 10,0 0)),((0 0,-10 0,0 -10,0 0)))'));

 st_nrings
-------------
 2