Hvad med dette:
with demo (data_date) as
( select 1072015 from dual union all
select 12017 from dual union all
select 612014 from dual union all
select 672013 from dual union all
select 72017 from dual union all
select 1112018 from dual )
select data_date
, to_char(data_date,'0000000')
, to_date(to_char(data_date,'0000000'),'DDDYYYY') as data_date_converted
from demo