mysql does not return alias names, so fall back

activerecord/lib/active_record/relation/calculations.rb

@@ -231,6 +231,8 @@ def execute_simple_calculation(operation, column_name, distinct) #:nodoc:
       # Postgresql doesn't like ORDER BY when there are no GROUP BY
       relation = reorder(nil)
 
+      column_alias = column_name
+
       if operation == "count" && (relation.limit_value || relation.offset_value)
         # Shortcut when limit is zero.
         return 0 if relation.limit_value == 0
@@ -241,16 +243,20 @@ def execute_simple_calculation(operation, column_name, distinct) #:nodoc:
 
         select_value = operation_over_aggregate_column(column, operation, distinct)
 
-        column_name = select_value.alias
+        column_alias = select_value.alias
         relation.select_values = [select_value]
 
         query_builder = relation.arel
       end
 
       result = @klass.connection.select_all(query_builder, nil, relation.bind_values)
-      row   = result.first
-      value = row && row.values.first
-      type_cast_calculated_value(value, result.column_types[column_name], operation)
+      row    = result.first
+      value  = row && row.values.first
+      column = result.column_types.fetch(column_alias) do
+        column_for(column_name)
+      end
+
+      type_cast_calculated_value(value, column, operation)
     end
 
     def execute_grouped_calculation(operation, column_name, distinct) #:nodoc: