ST_InteriorRingN-PolarDB(PolarDB)-阿里云帮助中心

Returns the Nth interior ring (hole) of a polygon as a LineString. Ring indexes start at 1.

Syntax

geometry ST_InteriorRingN(geometry aPolygon, integer n);

Parameter	Description
`aPolygon`	The input polygon.
`n`	The 1-based index of the interior ring to return.

Returns NULL if aPolygon is not a polygon geometry.
Returns NULL if the value of n is invalid.
Does not support MultiPolygon geometries. Use ST_Dump to decompose a MultiPolygon into individual polygons first.
Supports 3D geometries and preserves Z coordinates.

SELECT ST_AsText(ST_InteriorRingN('POLYGON((1 0,3 0,0 3,1 0),(1 0,2 0, 0 2,1 0))'::geometry, 1));

Output:

          st_astext
-----------------------------
 LINESTRING(1 0,2 0,0 2,1 0)
(1 row)