select tb.*,sum(流入- 流出)over(partition by 公司编码,银行编码 order by 时期 asc) from tb

------解决方案--------------------

SQL code

with t as (
select '20110000' a , '1001' b, '10' c, 1000 d, 0 e from dual
union all
select '20121210' a , '1001' b, '10' c, 20 d, 30 e from dual
union all
select '20121211' a , '1001' b, '10' c, 30 d, 100 e from dual
union all
select '20110000' a , '1002' b, '12' c, 800 d, 0 e from dual
union all
select '20121218' a , '1002' b, '12' c, 100 d, 90 e from dual
union all
select '20121219' a , '1002' b, '12' c, 200 d, 100 e from dual
)
select tt.a,tt.b,tt.c,decode(substr(tt.a,-4),'0000',tt.d,lag(tt.m) over(partition by tt.b,tt.c order by tt.a)),tt.d,tt.e,tt.m
from (
select t.a,t.b,t.c,t.d,t.e,sum(t.d-t.e)over(partition by t.b,t.c order by t.a) m from t ) tt

------解决方案--------------------

实测数据：
SQL code

CREATE TABLE T131
(
    Period VARCHAR2(20),
    CompCode VARCHAR2(20),
    BankCode VARCHAR2(20),
    InFlow  NUMBER(6),
    OutFlow NUMBER(6)
);

INSERT INTO T131 VALUES('20110000', '1001', '10', 1000, 0);
INSERT INTO T131 VALUES('20121210', '1001', '10', 20, 30);
INSERT INTO T131 VALUES('20121211', '1001', '10', 30, 100);

INSERT INTO T131 VALUES('20110000', '1002', '12', 800, 0);
INSERT INTO T131 VALUES('20111218', '1002', '12', 100, 90);
INSERT INTO T131 VALUES('20111219', '1002', '12', 200, 100);