curve-expression.ST_Length([ unit-name])

The ST_Length method returns the length of a curve in the units identified by the unit-name parameter. If the curve is empty, then NULL is returned.

If the curve contains Z values, these are not considered when computing the length of the geometry.

• ST_Length method for type ST_MultiCurve
• ST_Area method for type ST_Surface

The following example returns the result 2.

SELECT NEW ST_LineString( 'LineString(1 0, 1 1, 2 1)' ).ST_Length()

The following example creates a circularstring representing a half-circle and uses ST_Length to find the length of the geometry, returning the value PI.

SELECT NEW ST_CircularString( 'CircularString( 0 0, 1 1, 2 0 )' ).ST_Length()

The following example creates a linestring representing a path from Halifax, NS to Waterloo, ON, Canada and uses ST_Length to find the length of the path in metres, returning the result 1361967.76789.

SELECT NEW ST_LineString( 'LineString( -63.573566 44.646244, -80.522372 43.465187 )', 4326 )
		.ST_Length()

The following returns the lengths of the curves in the SpatialShapes table. The lengths are returned in Cartesian units.

SELECT ShapeID, TREAT( Shape AS ST_Curve ).ST_Length()
FROM SpatialShapes WHERE Shape IS OF ( ST_Curve )

The following example creates a linestring and an example unit of measure (example_unit_halfmetre). The ST_Length method finds the length of the geometry in this unit of measure, returning the value 4.0.

BEGIN
    DECLARE @curve ST_Curve;
    CREATE SPATIAL UNIT OF MEASURE IF NOT EXISTS  "example_unit_halfmetre" TYPE LINEAR CONVERT USING .5;
    SET @curve = NEW ST_LineString( 'LineString(1 0, 1 1, 2 1)' ) ;
    SELECT @curve.ST_Length('example_unit_halfmetre');
END