removed requirement to place singleton_value-group_by as the last group_by - added todo for a future refactoring

app/models/report/group_by/base.rb

@@ -59,8 +59,12 @@ class Report::GroupBy
 
     def define_group(sql)
       fields = all_group_fields
-      sql.group_by fields
-      sql.select fields
+      # fields usually are Strings which we want select and group_by
+      # sometimes fields are arrays of the form [String,String], where
+      # the fields.first is to select and where we have to group on field.last
+      #TODO: differenciate between all_group_fields and all_select_fields
+      sql.select fields.map   {|field| field.is_a?(String) ? field : field.first}
+      sql.group_by fields.map {|field| field.is_a?(String) ? field : field.last}
     end
   end
 end

app/models/report/group_by/singleton_value.rb

@@ -2,6 +2,12 @@ class Report::GroupBy
   class SingletonValue < Base
     dont_display!
 
+    def all_group_fields(prefix = true)
+      parent_fields = parent.all_group_fields if parent
+      #TODO: differenciate between all_group_fields and all_select_fields
+      (parent_fields || []) << ['1 as singleton_value', 'singleton_value']
+    end
+
     def define_group(sql)
       sql.select "1 as singleton_value"
       sql.group_by "singleton_value"