• ST_NumInteriorRing( poly ) , ST_NumInteriorRings( poly ) 

Returns the number of interior rings in the Polygon  value poly . 

ST_NumInteriorRing()  and ST_NuminteriorRings()  handle their arguments as described in the introduction to this section. 

## 12.17.7.5 GeometryCollection Property Functions 

mysql> SET @poly = ’Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))’; mysql> SELECT ST_NumInteriorRings(ST_GeomFromText(@poly)); +---------------------------------------------+ | ST_NumInteriorRings(ST_GeomFromText(@poly)) | +---------------------------------------------+ | 1 | +---------------------------------------------+ 

These functions return properties of GeometryCollection  values. 

Unless otherwise specified, functions in this section handle their geometry arguments as follows: 

•If any argument is NULL  or any geometry argument is an empty geometry, the return value is NULL . 

•If any geometry argument is not a syntactically well-formed geometry, an ER_GIS_INVALID_DATA  error occurs. 

•If any geometry argument is a syntactically well-formed geometry in an undefined spatial reference system (SRS), an ER_SRS_NOT_FOUND  error occurs. 

•Otherwise, the return value is non- NULL . 

These functions are available for obtaining geometry collection properties: 

• ST_GeometryN( gc , N ) 

Returns the N -th geometry in the GeometryCollection  value gc . Geometries are numbered beginning with 1. 

ST_GeometryN()  handles its arguments as described in the introduction to this section. 

mysql> SET @gc = ’GeometryCollection(Point(1 1),LineString(2 2, 3 3))’; mysql> SELECT ST_AsText(ST_GeometryN(ST_GeomFromText(@gc),1)); +-------------------------------------------------+ | ST_AsText(ST_GeometryN(ST_GeomFromText(@gc),1)) | +-------------------------------------------------+ | POINT(1 1) | +-------------------------------------------------+ 

• ST_NumGeometries( gc ) 

Returns the number of geometries in the GeometryCollection  value gc . 

ST_NumGeometries()  handles its arguments as described in the introduction to this section. 

mysql> SET @gc = ’GeometryCollection(Point(1 1),LineString(2 2, 3 3))’; mysql> SELECT ST_NumGeometries(ST_GeomFromText(@gc)); +----------------------------------------+ | ST_NumGeometries(ST_GeomFromText(@gc)) | +----------------------------------------+ | 2 | +----------------------------------------+ 

