select ss_customer_sk
     , sum(act_sales) sumsales
from (select ss_item_sk
           , ss_ticket_number
           , ss_customer_sk
           , case
                 when sr_return_quantity is not null then (ss_quantity - sr_return_quantity) * ss_sales_price
                 else (ss_quantity * ss_sales_price) end act_sales
      from store_sales
               left outer join store_returns on (sr_item_sk = ss_item_sk
          and sr_ticket_number = ss_ticket_number)
         , reason
      where sr_reason_sk = r_reason_sk
        and r_reason_desc = 'reason 28') t
group by ss_customer_sk
order by sumsales, ss_customer_sk limit 100