ST_InteriorRingN-ApsaraDB RDS(RDS)-阿里云帮助中心

Returns the Nth interior ring of a polygon as a LineString. Interior ring indexes start at 1.

Syntax

geometry ST_InteriorRingN(geometry aPolygon, integer n)

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

Returns NULL if aPolygon is not a polygon, or if n is invalid.
Does not support MultiPolygon geometries. To process a MultiPolygon, use ST_Dump to decompose it 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)