with gen_data as(
select 'M068406' as c,7 as len from dual union all select '2' as c,1 as len from dual union all
select 'M068407' as c,7 as len from dual union all select '44' as c,2 as len from dual union all
select '5' as c,1 as len from dual union all select '66' as c,2 as len from dual
)
,cte_add_2col as
(select rownum as id ,a.*,decode(len,7,c,null) as tmp_col from gen_data a)
select id, c,len
,last_value(tmp_col) ignore nulls over(order by id) as add_col
from cte_add_2col a
order by id;