Alias subquery used in calculations, to provide better compatibility with databases such as MonetDB

Signed-off-by: NMichael Koziarski <michael@koziarski.com>
Signed-off-by: NTom Ward <tom@popdog.net>
[#796 state:committed]

activerecord/lib/active_record/calculations.rb

@@ -211,7 +211,7 @@ def construct_calculation_sql(operation, column_name, options) #:nodoc:
 
           sql << " ORDER BY #{options[:order]} "       if options[:order]
           add_limit!(sql, options, scope)
-          sql << ')' if use_workaround
+          sql << ') AS #{aggregate_alias}_subquery' if use_workaround
           sql
         end