diff -r e564c255bf29 -r 0e82e7e5a34f server/sources/rql2sql.py
--- a/server/sources/rql2sql.py	Wed Jul 27 19:36:23 2011 +0200
+++ b/server/sources/rql2sql.py	Wed Jul 27 19:36:42 2011 +0200
@@ -1477,7 +1477,7 @@
                 rel._q_needcast = value
             return self.keyword_map[value]()
         if constant.type == 'Boolean':
-            return self.dbhelper.boolean_value(value)
+            return str(self.dbhelper.boolean_value(value))
         if constant.type == 'Substitute':
             try:
                 # we may found constant from simplified var in varmap