Variable Substitution in Postgis Query

[Maurizio Esposito]

Ciao Umberto
hi list
this is the query where substitution doesn't work:

DATA "the_geom from buildings"
FILTER "buildings.pk_id NOT IN (SELECT feat_id FROM feat_vis WHERE
feat_vis.ruolo='%ruolo%' AND feat_vis.layer='buildings')"

The table feat_vis is used as an exclusion list with the following
attributes:
ruolo
layer
feat_id

and if I substitute %ruolo% with a string value, i.e. 'technician' the
query works fine

Thank you

Maurizio