Syntax
------ 
ST_NumInteriorRings(poly)
NumInteriorRings(poly)
 
Description
----------- 
Returns an integer containing the number of interior rings
in the Polygon value poly.
 
Note that according the the OpenGIS standard, a POLYGON
should have exactly one ExteriorRing and all other rings
should lie within that ExteriorRing and thus be the
InteriorRings. Practically, however, some systems, including
MariaDB's, permit polygons to have several
'ExteriorRings'. In the case of there being multiple,
non-overlapping exterior rings ST_NumInteriorRings() will
return 1.
 
ST_NumInteriorRings() and NumInteriorRings() are synonyms.
 
Examples
-------- 
SET @poly = 'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2
1,1 1))';
 
SELECT NumInteriorRings(GeomFromText(@poly));
+---------------------------------------+
| NumInteriorRings(GeomFromText(@poly)) |
+---------------------------------------+
| 1 |
+---------------------------------------+
 
Non-overlapping 'polygon':
 
SELECT ST_NumInteriorRings(ST_PolyFromText('POLYGON((0 0,10
0,10 10,0 10,0 0),
 (-1 -1,-5 -1,-5 -5,-1 -5,-1 -1))')) AS NumInteriorRings;
 
+------------------+
| NumInteriorRings |
+------------------+
| 1 |
+------------------+
 

 
 
 
 
 
 
 

URL: https://mariadb.com/kb/en/st_numinteriorrings/