ST_InteriorRingN
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## Name

ST_InteriorRingN — Returns the Nth interior ring (hole) of a Polygon.

## Synopsis

`geometry ST_InteriorRingN(`geometry a_polygon, integer n`)`;

## Description

Returns the Nth interior ring (hole) of a POLYGON geometry as a LINESTRING. The index starts at 1. Returns NULL if the geometry is not a polygon or the index is out of range.

This function does not support MULTIPOLYGONs. For MULTIPOLYGONs use in conjunction with ST_GeometryN or ST_Dump

This method implements the OGC Simple Features Implementation Specification for SQL 1.1.

This method implements the SQL/MM specification. SQL-MM 3: 8.2.6, 8.3.5

This function supports 3d and will not drop the z-index.

## Examples

    SELECT ST_AsText(ST_InteriorRingN(geom, 1)) As geom
    FROM (SELECT ST_BuildArea(
    		ST_Collect(ST_Buffer(ST_Point(1,2), 20,3),
    			ST_Buffer(ST_Point(1, 2), 10,3))) As geom
    		)  as foo;

## See Also

ST_ExteriorRing, ST_BuildArea, ST_Collect, ST_Dump, ST_NumInteriorRing, ST_NumInteriorRings

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