ST_ToPolygon() method

Syntax

geometry-expression.ST_ToPolygon()

Returns

ST_Polygon If the geometry-expression is of type ST_Polygon, returns the geometry-expression. If the geometry-expression is of type ST_CurvePolygon, returns geometry-expression.ST_CurvePolyToPoly(). If the geometry-expression is a geometry collection with a single element of type ST_CurvePolygon, returns that element. If the geometry-expression is the empty set, returns an empty set of type ST_Polygon. Otherwise, raises an exception condition.

Examples

• Example 1 – The following example returns the result Polygon EMPTY.

  SELECT NEW ST_GeomCollection().ST_ToPolygon()

  The following returns an error because the Shape column is of type ST_Geometry and ST_Geometry does not support the ST_Area method.

  SELECT Shape.ST_Area()
  FROM SpatialShapes WHERE ShapeID = 22

  The following uses ST_ToPolygon to change the type of the Shape column expression to ST_Polygon. ST_Area returns the result 12.5.

  SELECT Shape.ST_ToPolygon().ST_Area()
  FROM SpatialShapes WHERE ShapeID = 22

  In this case, the value of the Shape column is known be of type ST_Polygon, so TREAT can be used to efficiently change the type of the expression. ST_Area returns the result 12.5.

  SELECT TREAT( Shape AS ST_Polygon ).ST_Area()
  FROM SpatialShapes WHERE ShapeID = 22

Standards

SQL/MM (ISO/IEC 13249-3: 2006) 5.1.33