Question

I have a query that is…

 SELECT m.msgFrom, m.msgTo, m.msgID, m.subject, m.dateTime, a.username 
 FROM mailbox m 
 JOIN accounts a ON (m.msgFrom = a.id) 
 WHERE msgTo = $user 
      OR msgFrom = $user 
      AND parentID = 0 
 ORDER BY dateTime DESC 
 LIMIT 250

Is it possible to change this query so that the ON changes depending on the value of msgTo or msgFrom.

I have a user variable. If the user variable equals msgTo get the username where the id equals msgFrom. If the user variable equals msgFrom get the username where the id equals msgTo?

I hope I explained it well enough?

Answer 1

You should be able to use an IF statement within the ON clause. This will join with the account of the opposite user. (i.e. if the message is from $user, then username will be for the receiving user and if the message is to $user, then username will be for the sending user.)

SELECT m.msgFrom, m.msgTo, m.msgID, m.subject, m.dateTime, a.username 
FROM mailbox m JOIN accounts a ON a.id=IF(msgTo=$user, msgFrom, msgTo)
WHERE msgTo = $user OR msgFrom = $user AND parentID = 0 
ORDER BY dateTime DESC LIMIT 250