Question

I have two tables like these:

USER
id
name

MESSAGE
id
sender_id
receiver_id

As you suppose, there are two one-to-many relations between those tables.

In my backend, I have filter to search for the messages associated to a user. After pressing “Filter”, I should show the list of messages associated to him/she, showing a column that specifies if the person was the sender or the receiver (or even both) of the message in a column called “Sender/Receiver”.

My doubt: I have also to give the possibility to order the list in base of the “Sender/Receiver” column. You know, pressing on “Sender/Receiver” column header will show first the messages where the user is “Sender”, then where is “Both” and finally where is “Receiver”. And pressing again will show the messages where the user is “Receiver”, then where is “Both” and then where is “Sender”.

What kind of SQL can do that ordering?

NOTE: the schema I proposed is not mandatory. If it is necessary propose another one.

Answer 1

ORDER
   BY CASE WHEN sender_id = [user-ID of interest]
            AND receiver_id = [user-ID of interest]
           THEN 2      -- is both sender & receiver
           WHEN sender_id = [user-ID of interest]
           THEN 1      -- is only sender
           ELSE 3      -- is only receiver
       END,
       [other conditions to sort by]