ST_CircularString If the geometry-expression is of type ST_CircularString, return the geometry-expression. If the geometry-expression is of type ST_CompoundCurve with a single element which is of type ST_CircularString, return that element. If the geometry-expression is a geometry collection with a single element of type ST_CircularString, return that element. If the geometry-expression is the empty set, return an empty set of type ST_CircularString. Otherwise, raise an exception condition.
Examples
Example 1 –
The following example returns the result CircularString (0 0, 1 1, 2 0).