The following bit of code should be reasonably self-explanatory but I was a little surprised to discover that there are no examples of doing this (for IBM i folks, at least) on the interwebnet.
So now there’s one.
insert into ignoreiln with slsrpt as (select * from ignoreiln where mtyp = 'SLSRPT'), invrpt as (select * from ignoreiln where mtyp = 'INVRPT') select a.mdir, 'INVRPT', a.siln, a.diln, a.riln, a.dept, a.brnd, 'Auto Created' from slsrpt a left outer join invrpt b on b.mdir = a.mdir and b.siln = a.siln and b.diln = a.diln and b.riln = a.riln and b.dept = a.dept and b.brnd = a.brnd where b.siln is null
If you want to know more, I would recommend starting with the IBM i Information Centre.