uden et enkelt primærnøglefelt, tror jeg, at dit bedste bud er:
select * from deal_status
inner join
(select deal_id as did, max(timestamp) as ts
from deal_status group by deal_id) as ds
on deal_status.deal_id = ds.did and deal_status.timestamp = ds.ts
dette vil stadig ikke fungere, hvis du tillader at have to forskellige statusser for det samme produkt på samme tid