How to make a mysql select for a specific table?

Question

MySQL

Greetings!
There is such a table (Fig. 1) which is a chat between two interlocutors.
It is necessary to make a selection so that it would be possible to see the latest messages from each group of two interlocutors (Fig. 2)
The difficulty lies in the fact that user_id 0 and user_id 1 are one user_id.

rice. 1

fig. 2

Answer 1

Make a selection of the time of the last record for each pair of subscribers and attach to it the same table for subscribers and time.

Answer 2

Select o.* from (
Select max(updated_at) as maxdate,  sender_user_id, recipient_user_id
from chattable 
group by sender_user_id, recipient_user_id
) as t
join chattable as o on t.sender_user_id=o.sender_user_id and t.recipient_user_id=o.recipient_user_id and t.maxdate=o.upadet_at

Instead of updated_at, you can use created_at or id
to filter users 0 and 1 more easily in a client script, php or other, or by an additional request for this selection