ST_NRings

Introduction: Returns the number of rings in a Polygon or MultiPolygon. Contrary to ST_NumInteriorRings, this function also takes into account the number of exterior rings.

This function returns 0 for an empty Polygon or MultiPolygon. If the geometry is not a Polygon or MultiPolygon, an IllegalArgument Exception is thrown.

Format: ST_NRings(geom: geometry)

Examples:

Input: POLYGON ((1 0, 1 1, 2 1, 2 0, 1 0))

Output: 1

Input: 'MULTIPOLYGON (((1 0, 1 6, 6 6, 6 0, 1 0), (2 1, 2 2, 3 2, 3 1, 2 1)), ((10 0, 10 6, 16 6, 16 0, 10 0), (12 1, 12 2, 13 2, 13 1, 12 1)))'

Output: 4

Input: 'POLYGON EMPTY'

Output: 0

Input: 'LINESTRING (1 0, 1 1, 2 1)'

Output: Unsupported geometry type: LineString, only Polygon or MultiPolygon geometries are supported.