自定义函数引发的性能问题

---执行1次
select count(1)
  from LOAN_DUEBILLDATA bd
  left join LOAN_CONTRACTDATA bc
    on bd.RelativeSerialNo2 = bc.SerialNo
 where nvl(bd.ActualMaturity, bd.Maturity) <= '2014/08/06'
   and nvl(bd.ActualMaturity, bd.Maturity) >= '2014/07/07'
   and (bd.FinishDate is null or bd.FinishDate = '')
   and (bc.ManageUserID = '00717' or
        getCustomerManager(bc.CustomerId) = '00717')
----返回4条记录

---getCustomerManager函数里的sql执行3619次
SELECT USERID FROM CUSTOMER_BELONG WHERE CUSTOMERID = :B1 AND BELONGATTRIBUTE='1'


select  count(1)
  from LOAN_DUEBILLDATA bd
  left join LOAN_CONTRACTDATA bc
    on bd.RelativeSerialNo2 = bc.SerialNo
 where nvl(bd.ActualMaturity, bd.Maturity) <= '2014/08/06'
   and nvl(bd.ActualMaturity, bd.Maturity) >= '2014/07/07'
   and (bd.FinishDate is null or bd.FinishDate = '')
   and (bc.ManageUserID = '00717' or
        getCustomerManager(bc.CustomerId) = '00717');


初步改写为:
select count(1)
  from LOAN_DUEBILLDATA bd, LOAN_CONTRACTDATA bc, (select CustomerId FROM CUSTOMER_BELONG WHERE BELONGATTRIBUTE='1') be
 where bd.RelativeSerialNo2 = bc.SerialNo(+)
   and nvl(bd.ActualMaturity, bd.Maturity) <= '2014/08/06'
   and nvl(bd.ActualMaturity, bd.Maturity) >= '2014/07/07'
   and (bd.FinishDate is null or bd.FinishDate = '')
   and be.CustomerId = bc.CustomerId
   and (bc.ManageUserID = '00717' or be.customerid = '00717')