with t as (
  select 1 id_rec, 1 pr from dual union all
  select 2 id_rec, 1 pr from dual union all
  select 3 id_rec, 2 pr from dual union all
  select 4 id_rec, 3 pr from dual union all
  select 5 id_rec, 4 pr from dual union all
  select 6 id_rec, 8 pr from dual
  )
select id_rec, decode(v, 1, pr) pr
from t,
lateral(select rownum v from dual connect by level <= 5 - pr);

    ID_REC         PR
---------- ----------
         1          1
         1
         1
         1
         2          1
         2
         2
         2
         3          2
         3
         3
         4          3
         4
         5          4
         6          8

15 rows selected.

with t as (
  select 1 id_rec, 1 pr from dual union all
  select 2 id_rec, 1 pr from dual union all
  select 3 id_rec, 2 pr from dual union all
  select 4 id_rec, 3 pr from dual union all
  select 5 id_rec, 4 pr from dual union all
  select 6 id_rec, 8 pr from dual
  )
select id_rec, decode(level, 1, pr) pr
from t
start with id_rec is not null
connect by prior id_rec = id_rec and prior dbms_random.value is not null and level <= 5 - pr;

    ID_REC         PR
---------- ----------
         1          1
         1
         1
         1
         2          1
         2
         2
         2
         3          2
         3
         3
         4          3
         4
         5          4
         6          8

15 rows selected.

with t as (
  select 1 id_rec, 1 pr from dual union all
  select 2 id_rec, 1 pr from dual union all
  select 3 id_rec, 2 pr from dual union all
  select 4 id_rec, 3 pr from dual union all
  select 5 id_rec, 4 pr from dual union all
  select 6 id_rec, 8 pr from dual
  )
select *
from t
model unique single reference
partition by (id_rec)
dimension by (1 rn)
measures (pr)
rules upsert iterate(4) until (iteration_number > 3 - pr[1])
(pr[iteration_number + 1] = pr[cv()]
)
order by id_rec, rn;

    ID_REC         RN         PR
---------- ---------- ----------
         1          1          1
         1          2
         1          3
         1          4
         2          1          1
         2          2
         2          3
         2          4
         3          1          2
         3          2
         3          3
         4          1          3
         4          2
         5          1          4
         6          1          8

15 rows selected.

with t as (
  select 1 id_rec, 1 pr from dual union all
  select 2 id_rec, 1 pr from dual union all
  select 3 id_rec, 2 pr from dual union all
  select 4 id_rec, 3 pr from dual union all
  select 5 id_rec, 4 pr from dual union all
  select 6 id_rec, 8 pr from dual
  ),
 s (id_rec, pr, lvl) as
 (select id_rec, pr, 1 lvl
  from t
  union all
  select s.id_rec, s.pr, s.lvl + 1
  from t, s
  where s.id_rec = t.id_rec and s.lvl <= 4 - t.pr
 )
select id_rec, decode(lvl, 1, pr) pr
from s
order by id_rec, pr;

    ID_REC         PR
---------- ----------
         1          1
         1
         1
         1
         2          1
         2
         2
         2
         3          2
         3
         3
         4          3
         4
         5          4
         6          8

15 rows selected.