MySQL join with two potential field names - mysql

Question

For a website I'm working on I was tasked with implementing a private messaging system.
My basic scenario here is, there are several message entries in the database, each containing a sender and a recipient. However, the "current user" should be able to see both those messages, as they are both relevant to him.
The problem is, I am only interested in the data of the other user, not my own. But the "current user" can be both the sender or the recipient.
My query down here gets this job done, but it is hardly elegant. I am joining both users, then deciding using an IF which data I should get.
SELECT
IF(m.sender = ?, 1, 0) AS isself,
IF(m.sender = ?, u_recipient.id, u_sender.id) AS other_id,
IF(m.sender = ?, u_recipient.displayName, u_sender.displayName) AS other_name,
IF(m.sender = ?, u_recipient_avatar.url, u_sender_avatar.url) AS other_avatar,
m.text AS text
FROM messages AS m
LEFT JOIN user AS u_sender
ON u_sender.id = m.sender
LEFT JOIN avatars AS u_sender_avatar
ON u_sender_avatar.id = u_sender.avatarId
LEFT JOIN user AS u_recipient
ON u_recipient.id = m.recipient
LEFT JOIN avatars AS u_recipient_avatar
ON u_recipient_avatar.id = u_recipient.avatarId
WHERE ( m.sender = ? OR m.recipient = ? )
AND UNIX_TIMESTAMP(m.timestamp) > ?
ORDER BY m.timestamp ASC
LIMIT 100
So basically, my question here is, is there any more elegant way of doing this? Storing the sender/recipient int into 1 single table to be reused in the join? Otherwise, is this a performance hog (joining tables I don't need?). Or should I just take care of seperating these in the application itself?
Thanks in advance!

Answer 1

Seeing that I am not allowed to edit the other answer, which was partially correct.
My answer here is based on Ben's, however, with the syntax errors removed.
SELECT d.isself, other_id, u.displayName AS other_name, a.url AS other_avatar, text
FROM
(
SELECT 0 AS isself, m.sender AS other_id, m.timestamp, m.text
FROM messages AS m
WHERE m.recipient = ?
UNION
SELECT 1 AS isself, m.recipient AS other_id, m.timestamp, m.text
FROM messages AS m
WHERE m.sender = ?
) AS d
LEFT JOIN user AS u
ON u.id = d.other_id
LEFT JOIN avatars AS a
ON a.id = u.avatarId
WHERE UNIX_TIMESTAMP(timestamp) > ?
ORDER BY m.timestamp ASC
LIMIT 100

Answer 2

How about something like:
SELECT isself, other_id, u.displayName AS other_name, a.url AS other_avatar, text
FROM
(
SELECT 0 AS isself, m.sender AS other_id, m.timestamp, m.text
FROM messages AS m
WHERE m.recipient = ?
UNION
SELECT 1 AS isself, m.recipient AS other_id, m.timestamp, m.text
FROM messages AS m
WHERE m.sender = ?
) AS d
LEFT JOIN user AS u
ON u.id = d.other_id
LEFT JOIN avatars AS a
ON a.id = u.avatarId
WHERE UNIX_TIMESTAMP(timestamp) > ?
LIMIT 100
If the message's sender and recipient IDs will always be found in the user table, the "LEFT JOIN user" should be changed to an inner join--"JOIN user". If each user has an avatar entry, then that left join should also be changed to an inner join.