NumRings (geography Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns the total number of rings in a Polygon instance. In the SQL Server geography type, external and internal rings are not distinguished, as any ring can be taken to be the external ring.
Syntax
.NumRings ()
Return Type
SQL Server return type: int
CLR return type: SqlInt32
Remarks
This method will return NULL if this is not a Polygon instance and will return 0 if the instance is empty. This method is precise.
Examples
This example creates a Polygon instance with two rings and confirms that it has two rings.
DECLARE @g geography;
SET @g = geography::STGeomFromText('POLYGON((-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653), (-122.357 47.654, -122.357 47.657, -122.349 47.657, -122.349 47.650, -122.357 47.654))', 4326);
SELECT @g.NumRings();