item.cc:

              Item_ref to point to the Item in the select list and replace the

              Item_field created by the parser with the new Item_ref.

            */

            Item_ref *rf= new Item_ref(db_name,table_name,field_name);

            Item_ref *rf= new Item_ref(context, db_name,table_name,field_name);

            if (!rf)

              return 1;

            thd->change_item_tree(ref, rf);

            thd->change_item_tree(reference, rf);

            /*

              Because Item_ref never substitutes itself with other items 

              in Item_ref::fix_fields(), we can safely use the original 

              pointer to it even after fix_fields()

             */

            return rf->fix_fields(thd, tables, ref) ||  rf->check_cols(1);

            return rf->fix_fields(thd, reference) ||  rf->check_cols(1);

          }

        }

      }