In my database I calculate distance between nodes with: SELECT DISTINCT dest.name, AsText(orig.location), AsText(dest.location), round((glength(linestringfromwkb(linestring((orig.location), (dest.location)))))) as distance FROM nodes orig, nodes dest WHERE orig.name='GERP' I would like to add "and distance < dest.visibility" at the end, but am told that distance is an unknown column. Any insight very much appreciated.