PostGIS
Description
If the geometry is a polygon or multi-polygon returns the number of rings. Unlike NumInteriorRings, it counts the outer rings as well.
This
function supports 3d and will not drop the z-index.
This
method supports Circular Strings and Curves.
Examples
SELECT ST_NRings(geom) As Nrings, ST_NumInteriorRings(geom) As ninterrings
FROM (SELECT ST_GeomFromText('POLYGON((1 2, 3 4, 5 6, 1 2))') As geom) As foo;
nrings | ninterrings
--------+-------------
1 | 0
(1 row)