select a.pkey, a.ptno, b.qty1, a.seq, a.qty2
from tableb a
left outer join
(
    select a.pkey, b.seq, a.qty1
    from tablea a,
    (
        select pkey, min(seq) seq
        from tableb
        group by pkey
    ) b
    where a.pkey = b.pkey
) b
on a.pkey = b.pkey and a.seq = b.seq

하단의 합은

union all 로 처리하면 될듯합니다

답변 감사합니다.