STPolyFromText (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns a geometry instance from an Open Geospatial Consortium (OGC) Well-Known Text (WKT) representation augmented with any Z (elevation) and M (measure) values carried by the instance.
Syntax
STPolyFromText ( 'polygon_tagged_text' , SRID )
Arguments
polygon_tagged_text
Is the WKT representation of the geometryPolygon instance you wish to return. polygon_tagged_text is an nvarchar(max) expression.
SRID
Is an int expression representing the spatial reference ID (SRID) of the geometryPolygon instance you wish to return.
Return Types
SQL Server return type: geometry
CLR return type: SqlGeometry
OGC type: Polygon
Remarks
This method will throw a FormatException if the input is not well-formatted.
Examples
The following example uses STPolyFromText() to create a geometry instance.
DECLARE @g geometry;
SET @g = geometry::STPolyFromText('POLYGON ((5 5, 10 5, 10 10, 5 5))', 0);
SELECT @g.ToString();