Name
ST_NumInteriorRings — 返回多边形的内环(孔)数。
Synopsis
integer
ST_NumInteriorRings
(
geometry
a_polygon
)
;
描述
返回多边形几何体的内环数量。如果几何体不是多边形，则返回NULL。
This method implements the SQL/MM specification. SQL-MM 3：8.2.5
已更改：2.0.0-在以前的版本中，它允许传递MULTIPOLYGON，返回第一个多边形的内部环数。
示例
--If you have a regular polygon
SELECT gid, field1, field2, ST_NumInteriorRings(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(geom)) AS numholes
FROM (SELECT gid, field1, field2, (ST_Dump(geom)).geom As geom
FROM sometable) As foo
GROUP BY gid, field1,field2;