diff -r d773589b6d46 -r 73bd5012336f server/sqlutils.py
--- a/server/sqlutils.py	Tue Jan 07 15:48:31 2014 +0100
+++ b/server/sqlutils.py	Thu Nov 14 12:26:29 2013 +0100
@@ -327,10 +327,10 @@
 
     class group_concat(object):
         def __init__(self):
-            self.values = []
+            self.values = set()
         def step(self, value):
             if value is not None:
-                self.values.append(value)
+                self.values.add(value)
         def finalize(self):
             return ', '.join(unicode(v) for v in self.values)