Create table x_test (
bill_num varchar2(50),
inv_num varchar2(50),
inv_date date,
amount number
);

Insert into x_test values ('101','5001',to_date('09-02-2012','mm-dd-yyyy'),30);

Insert into x_test values ('101','5002',to_date('09-02-2013','mm-dd-yyyy'),20);

Insert into x_test values ('101','5003',to_date('09-02-2014','mm-dd-yyyy'),60);

Insert into x_test values ('101','5004',to_date('09-02-2015','mm-dd-yyyy'),100);


Insert into x_test values ('201','6001',to_date('07-02-2012','mm-dd-yyyy'),200);

Insert into x_test values ('201','6002',to_date('07-02-2013','mm-dd-yyyy'),40);

Insert into x_test values ('201','6003',to_date('07-02-2014','mm-dd-yyyy'),90);

Insert into x_test values ('201','6004',to_date('07-02-2015','mm-dd-yyyy'),80);

SELECT Bill_num,
         Inv_num,
         Inv_date,
         SUM (
            Amount)
         OVER (PARTITION BY Bill_num
               ORDER BY Inv_date
               ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING)
            SUM
    FROM X_test
   WHERE Bill_num = '101'
ORDER BY Inv_date DESC;



BILL_NUM   INV_NUM        INV_DATE         SUM
---------- -------------- --------- ----------
101        5004           02-SEP-15        110
101        5003           02-SEP-14         50
101        5002           02-SEP-13         30
101        5001           02-SEP-12