ST_NRings — Returns the number of rings in a polygonal geometry.


integer ST_NRings(geometry geomA);


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.


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)