Question

i’m working on a private messaging system , it looks more like a social networks messaging . there is no title and related pms are shown like forum threads .

i have two table to keep tracks of the pms

pm_sessions  : pm_session  , sender , receiver, pm_counter 

pm           : id , pm_session  , text , date , sender

pm_session works like a wrapper for pm

now in the user profile i want to show list of the users whos been sending or receiving pm from current user

the problem is i don’t want to show receiver and sender users separately , i want to have all of the users whos been talking to my guy in one list

here is what i got in mind ,and i now it doesn’t work like this with all IF statements

$current_user = $_session['userid'];
    $query = " 

 select pms.sender , pms.receiver, 
 count(pms.otheruser) as total_dialogs_with_this_user , 
 u.username as other_user_name  , u.id as other_user_id

 from pm_session pms

   //// joining to the users table on the other user id
   if($current_user = pms.sender)
     JOIN users u on pms.receiver= u.id 
   if($current_user = pms.receiver)
     JOIN users u on  pms.sender = u.id 

  WHERE pms.reciver = $current_user || pms.sender = $current_user

   /// grouping by other user id
   if($current_user = pms.sender)
     group by pms.receiver
   if($current_user = pms.receiver)
     group by pms.sender ";

i expect results to be something like

HELLO max ... you have been talking to :

ross... 3 dialogs
joey ... 4 dialogs
chandler ... 5 dialogs

i can easily write this with two query , one for receiver and one for senders
but like i said i dont want to separate them

Answer 1

SELECT   CASE $current_user
           WHEN pms.sender   THEN pms.receiver
           WHEN pms.receiver THEN pms.sender
         END                  AS other_user_id,
         u.username           AS other_user_name,
         COUNT(pms.otheruser) AS total_dialogs_with_this_user
FROM     pm_session           AS pms
  JOIN   users                AS u
           ON u.id = CASE $current_user
             WHEN pms.sender   THEN pms.receiver
             WHEN pms.receiver THEN pms.sender
           END
GROUP BY other_user_id, other_user_name