distance between two points

[Lukasz Nowak]

Hi, I have some problems with detecting distance by lenght of LineString

AsBinary() is working well but when I want to create LineStringFromWKB I recieve only NULL

it is my sql:

SELECT ROUND( GLength( LineStringFromWKB( LineString( AsBinary( a.g ) , AsBinary( b.g ) ) ) ) ) AS dis
FROM cities a, cities b
WHERE a.name = 'Zakopane'
AND b.name = 'Warszawa'

-------
dis
NULL


PLEASE HELP