others (#15) - assign_vertex_id (#264) - Message List

I have prepared by adding source, target, and length columns for my data: ALTER TABLE quan10 ADD COLUMN source integer;

ALTER TABLE quan10 ADD COLUMN target integer;

ALTER TABLE quan10 ADD COLUMN length double precision;

but when i run:

SELECT assign_vertex_id('quan10', 0.001, 'the_geom', 'gid'); i alway receive a resuilt: cannot EXECUTE a null querystring Tell me what's happend, please.