rownum理解
select *
from (select rownum bb,aa.*
from (select bb.*, cf.dtdiscountdate, cf.mdiscountrate
from Loan_DiscountContractBill bb, loan_contractform cf
where 1 = 1
and bb.ncontractid = cf.id
and to_char(bb.dtEnd,'yyyy-mm-dd') > '2010-03-31'
-- (select to_char(sysdate+15,'yyyy-mm-dd') from dual)
and bb.nContractId > 0
and bb.nstoragestatusid = 1
order by bb.nContractID, bb.nSerialNo) aa)