Oracle SQL cara mengelompokkan, tetapi memiliki beberapa baris jika grup diulang di kemudian hari

Ini adalah masalah kesenjangan dan pulau. Ada pendekatan yang berbeda, tetapi yang sederhana menggunakan perbedaan nomor baris:

with paaf as (<your first query here>
     )
select paaf.assignment_id,
       paaf.position_id,
       min(paaf.effective_start_date) as effective_start_date,
       max(paaf.effective_end_date) as effective_end_date
from (select paaf.*,
             row_number() over (order by effective_start_date) as seqnum,
             row_number() over (partition by position_id order by effective_start_date) as seqnum_p
      from paaf
     ) paaf
group by (seqnum - seqnum_p), position_id, assignment_id;