select buyer_name,currency,sum(net_amt) net_amt
from
(
    select m.buyer_name,n.OLD_INVOICE_NO,n.despatch_date invoice_date,
    (
      SELECT B.CUR_abbr  FROM MREL.MREL_CURRENCY_MASTER B,SALES.SALES_SALEADV_MASTER A
        WHERE A.SALE_ADV_NO=( select y.MILL_ORDER_NO from SALES_EXPORT_INVOICE_QUALITY y,sales_export_invoice_master x 
        where x.despatch_code = y.despatch_code
        and x.comp_code = y.comp_code
        and x.old_invoice_no = n.old_invoice_no
        and rownum <= 1)
        AND A.COMP_CODE = 3 
        AND B.CURR_CODE = A.CURR_CODE
    ) currency
    , n.net_amount NET_AMT from sales_export_invoice_master n,mrel.MREL_SALES_BUYER_MAST m
    where n.buyer_code = m.buyer_code
    and n.despatch_date between '01-APR-2009' AND '31-DEC-2009'
    ORDER BY 1
)
group by buyer_name,currency
order by 1