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ST_ExteriorRing

Returns the exterior ring of a Polygon. This function extracts the outer boundary of the polygon as a LineString geometry.

Syntax

ST_ExteriorRing(poly)
ExteriorRing(poly)

Description

Returns the exterior ring of the Polygon value poly as a LineString.

ST_ExteriorRing() and ExteriorRing() are synonyms.

Examples

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SET @poly = 'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))';

SELECT AsText(ExteriorRing(GeomFromText(@poly)));
+-------------------------------------------+
| AsText(ExteriorRing(GeomFromText(@poly))) |
+-------------------------------------------+
| LINESTRING(0 0,0 3,3 3,3 0,0 0)           |
+-------------------------------------------+