select ...
from filea a
left join fileb b on a.key=b.key
where b.key is null

oder

select ...
from filea a
exception join fileb b on a.key=b.key

oder

select ...
from file a
where not exists (select * from fileb b where a.key=b.key)

oder

:
:

Jetzt musst du nur noch kombinieren

insert into zfile (f1, f2, ...)
values(
select ....
where ....
)