with per as (
  select trunc(min(bdate), 'month') strt,
  last_day(max(bdate)) fin,
  min(balance-cr+db) keep (DENSE_RANK FIRST ORDER BY bdate) start_bal -- остаток на последний день предыдущего месяца
  from BALANCES
),
dates as (
select strt + level - 1 bdate
from per 
connect by level < fin - strt + 2
),
date_bal as (
  select d.bdate from dates d
)
select d.bdate, nvl(b.cr, 0), nvl(b.db,0), nvl(last_value(b.balance) ignore nulls over (order by d.bdate), per.start_bal) balance,  per.start_bal
from date_bal d
left join balances b
on b.bdate = d.bdate
cross join per
order by bdate

with per as (
  select trunc(min(bdate), 'month') strt,
  last_day(max(bdate)) fin,
  min(balance-cr+db) keep (DENSE_RANK FIRST ORDER BY bdate) start_bal -- остаток на последний день предыдущего месяца
  from BALANCES
),
dates as (
select strt + level - 1 bdate
from per 
connect by level < fin - strt + 2
)
select d.bdate, nvl(b.cr, 0), nvl(b.db,0), nvl(last_value(b.balance) ignore nulls over (order by d.bdate), per.start_bal) balance,  per.start_bal
from dates d
left join balances b
on b.bdate = d.bdate
cross join per
order by bdate

CREATE TABLE BALANCES
(ID NUMBER NOT NULL,
ACCT_ID NUMBER NOT NULL,
BDATE DATE NOT NULL,
CR NUMBER (20,2),
DB NUMBER (20,2),
BALANCE NUMBER (20,2));

INSERT INTO BALANCES VALUES (1, 1, TO_DATE('15-01-2016','DD-MM-YYYY'), 1000.00, 0.00, 1000.00);
INSERT INTO BALANCES VALUES (2, 1, TO_DATE('22-01-2016','DD-MM-YYYY'), 600.00, 300.00, 1300.00);
INSERT INTO BALANCES VALUES (3, 1, TO_DATE('04-02-2016','DD-MM-YYYY'), 100.00, 0.00, 1400.00);
INSERT INTO BALANCES VALUES (4, 1, TO_DATE('29-02-2016','DD-MM-YYYY'), 0.00, 200.00, 1200.00);

INSERT INTO BALANCES VALUES (5, 2, TO_DATE('12-01-2016','DD-MM-YYYY'), 20.00, 6.00, 14.00);
INSERT INTO BALANCES VALUES (6, 2, TO_DATE('22-01-2016','DD-MM-YYYY'), 100.00, 50.00, 64.00);

-- остаток может быть и до периода - пришло 200, а 300 уже было
INSERT INTO BALANCES VALUES (7, 3, TO_DATE('04-02-2016','DD-MM-YYYY'), 200.00, 0.00, 500.00);
INSERT INTO BALANCES VALUES (8, 3, TO_DATE('05-02-2016','DD-MM-YYYY'), 0.00, 100.00, 400.00);
INSERT INTO BALANCES VALUES (9, 3, TO_DATE('06-02-2016','DD-MM-YYYY'), 200.00, 600.00, 0.00);

INSERT INTO BALANCES VALUES (10, 4, TO_DATE('29-01-2016','DD-MM-YYYY'), 10000.00, 4000.00, 6000.00);
INSERT INTO BALANCES VALUES (11, 4, TO_DATE('04-02-2016','DD-MM-YYYY'), 11111.00, 0.00, 17611.00);

commit;

-- счета
with per_acc as (
  select 
    acct_id acct_id,
    min(bdate) strt, 
    max(bdate) fin
    from BALANCES
  group by acct_id
),

-- самое первое и самое последнее числа месяца
per as (
  select
    trunc(min(strt), 'month') strt,
    last_day(max(fin)) fin
  from per_acc pa

),

-- счет, остаток на утро начала периода
acc_strt as (
    select 
        pa.acct_id,
        b.balance - b.cr + b.db strt_bal -- остаток на последнее число предыдущего месяца
       from per_acc pa
       inner join balances b
       on b.acct_id = pa.acct_id
       and b.bdate = pa.strt
),

-- все даты в периоде
dates as (
select strt + level - 1 bdate 
from per 
connect by level < fin - strt + 2
)

-- собственно выборка
select 
    acc_st.acct_id,
    d.bdate,
    nvl(b.cr, 0),
    nvl(b.db,0), 
    nvl(last_value(b.balance) ignore nulls over (partition by acc_st.acct_id order by d.bdate), acc_st.strt_bal) balance 

from acc_strt acc_st

cross join dates d

left join balances b
on b.bdate = d.bdate 
and b.acct_id = acc_st.acct_id 

cross join per

order by acc_st.acct_id, d.bdate

cross join per

INSERT INTO BALANCES VALUES (7, 3, TO_DATE('04-02-2016','DD-MM-YYYY'), 200.00, 0.00, 500.00);