Postgis point table

[Stéphane RIFF]

I have a postgis point table, display GPS coordinate in WGS84.
It works well with mapserver.
But now i'd like to show those points in a LINE type layer with mapserver
but i can't figure how to do it :

i've tried this in mapfile :

  DATA
"geometryfromtext(replace(astext(geomunion(geom)),'MULTIPOINT(','LINESTRING('),4326)
from <tablename>;"

but mapserver failed to draw the layer.
Does somebody already do something like that ???
Thanks