Description

Return the number of interior rings of a polygon geometry. Return NULL if the geometry is not a polygon.

This method implements the SQL/MM specification. SQL-MM 3: 8.2.5

Changed: 2.0.0 - in prior versions it would allow passing a MULTIPOLYGON, returning the number of interior rings of first POLYGON.

Examples

Count the interior rings of a Polygon.

SELECT gid, field1, field2, ST_NumInteriorRings(geom) AS numholes
FROM sometable;

For a MultiPolygon, dump its component Polygons and sum their interior ring counts.

SELECT gid, field1, field2, SUM(ST_NumInteriorRings(geom)) AS numholes
FROM (
    SELECT gid, field1, field2, (ST_Dump(geom)).geom AS geom
    FROM sometable
) AS foo
GROUP BY gid, field1, field2;
            

See Also

ST_NumInteriorRing, ST_InteriorRingN