Returns the length measurement of the ST_MultiCurve value. The result is measured in the units specified by the parameter.
SELECT NEW ST_MultiCurve( NEW ST_LineString('LineString (0 0, 1 0)' ), NEW ST_CircularString( 'CircularString( 0 0, 1 1, 2 0)' ) ) .ST_Length()
The following example returns the name and length of all roads longer than 100 miles. This example assumes the road table exists, that the geometry column has type ST_MultiCurve or ST_MultiLineString, and the sa_install_feature system procedure has been used to load the st_geometry_predefined_uom.
SELECT name, geometry.ST_Length( 'Statute Mile' ) len FROM roads WHERE len > 100
SQL/MM (ISO/IEC 13249-3: 2006) 9.3.4