Cara mengambil pesan yang dikelompokkan berdasarkan tanggal SQL

Anda sepertinya menginginkan yang berbeda daftar orang yang diajak bicara Dave:

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;