Hur man hämtar grupperade meddelanden sorterade efter datum SQL

Du verkar vilja ha det distinkt lista över personer som Dave pratar med:

select (case when receiver = 'Dave' then Sender else Receiver end)
from messages m
where 'Dave' in (Receiver, Sender)
group by (case when receiver = 'Dave' then Sender else Receiver end)
order max(date) desc;