ST_ToLineString() method

Syntax

geometry-expression.ST_ToLineString()

Returns

ST_LineString If the geometry-expression is of type ST_LineString, return the geometry-expression. If the geometry-expression is of type ST_CircularString or ST_CompoundCurve, return geometry-expression.ST_CurveToLine(). If the geometry-expression is a geometry collection with a single element of type ST_Curve, return that element cast as ST_LineString. If the geometry-expression is the empty set, return an empty set of type ST_LineString. Otherwise, raise an exception condition.

Examples

• Example 1 – The following returns an error because the Shape column is of type ST_Geometry and ST_Geometry does not support the ST_Length method.

  SELECT Shape.ST_Length()
  FROM SpatialShapes WHERE ShapeID = 5

  The following uses ST_ToLineString to change the type of the Shape column expression to ST_LineString. ST_Length returns the result 7.

  SELECT Shape.ST_ToLineString().ST_Length()
  FROM SpatialShapes WHERE ShapeID = 5

  In this case, the value of the Shape column is known be of type ST_LineString, so TREAT can be used to efficiently change the type of the expression. ST_Length returns the result 7.

  SELECT TREAT( Shape AS ST_LineString ).ST_Length()
  FROM SpatialShapes WHERE ShapeID = 5

Standards

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