MySQL:

ST_NUMINTERIORRINGS

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.

URL: https://dev.mysql.com/doc/refman/8.0/en/gis-polygon-property-functions.html

Example

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 |
+---------------------------------------------+