Name
ST_NumInteriorRings — Return the number of interior rings of the first polygon in the geometry. This will work with both POLYGON and MULTIPOLYGON types but only looks at the first polygon. Return NULL if there is no polygon in the geometry.
Synopsis
integer ST_NumInteriorRings(geometry a_polygon);
Description
Return the number of interior rings of the first polygon in the geometry. This will work with both POLYGON and MULTIPOLYGON types but only looks at the first polygon. Return NULL if there is no polygon in the geometry.
This method implements the SQL/MM specification: SQL-MM 3: 8.2.5
Examples
--If you have a regular polygon SELECT gid, field1, field2, ST_NumInteriorRings(the_geom) AS numholes FROM sometable; --If you have multipolygons --And you want to know the total number of interior rings in the MULTIPOLYGON SELECT gid, field1, field2, SUM(ST_NumInteriorRings(the_geom)) AS numholes FROM (SELECT gid, field1, field2, (ST_Dump(the_geom)).geom As the_geom FROM sometable) As foo GROUP BY gid, field1,field2;