STGeometryN (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns a specified geometry in a geometry collection.
Syntax
.STGeometryN ( expression )
Arguments
expression
Is an int expression between 1 and the number of geometry instances in the geometrycollection.
Return Types
SQL Server return type: geometry
CLR return type: SqlGeometry
Remarks
This method returns null if the parameter is larger than the result of STNumGeometries() and will throw an ArgumentOutOfRangeException if the expression parameter is less than 1.
Examples
The following example creates a MultiPoint``geometry collection and uses STGeometryN() to find the second geometry instance of the collection.
DECLARE @g geometry;
SET @g = geometry::STGeomFromText('MULTIPOINT(0 0, 13.5 2, 7 19)', 0);
SELECT @g.STGeometryN(2).ToString();