ST_ExteriorRing

Introduction: Returns a LINESTRING representing the exterior ring (shell) of a POLYGON. Returns NULL if the geometry is not a polygon.

Format: ST_ExteriorRing(A: Geometry)

Since: v1.2.1

Example:

SELECT ST_ExteriorRing(ST_GeomFromText('POLYGON((0 0 1, 1 1 1, 1 2 1, 1 1 1, 0 0 1))'))

Output:

LINESTRING (0 0, 1 1, 1 2, 1 1, 0 0)