Name
ST_NRings — Returns the number of rings in a polygonal geometry.
Synopsis
integer ST_NRings(geometry geomA);
Descrizione
If the geometry is a polygon or multi-polygon returns the number of rings. Unlike NumInteriorRings, it counts the outer rings as well.
Questa funzione supporta il 3d e non distrugge gli z-index.
Questo metodo supporta le Curve e le Circular String.
Esempi
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)