SQL query for a set of 2 users

Question

I have a table in my database saving messages between users.

The table "dt_inbox" has the following structure :
- messageid (PK)
- fromid => message initiated by userid=A
- toid => message sent to userid=B
- conversationid => id of the conversation
- datesent => date of message sent
- inbox_view => flag 0 or 1 to know if message has been read
- inboxdelete => flag 0 or 1 to know if message has been deleted

I'm trying to create a query in order to have a list of all messages for userid A: - sent by user A to user B(C,D,E...) , or sent by user B (C,D,E...) to user A => message sent fromid A -> toid B or fromid B -> toid A should appear in one line.
- each couple of users fromid/toid should appear in one line.
- showing datemax(datesent) of last message between user A and B
- ordered by datemax
- inboxdeleted = 0 and inbox_view=0.

Here is the query I have, but the result is not as expected, for userid = 12 :

SELECT messageid, conversationid, fromid, toid,
                (SELECT MAX(datesent) FROM dt_inbox dd WHERE dd.conversationid =     d.conversationid) as datemax,
                (SELECT count(*) FROM dt_inbox dd WHERE dd.conversationid=d.conversationid) as messagesnr,
                (SELECT count(*) FROM dt_inbox dd WHERE dd.conversationid=d.conversationid AND dd.inboxview=0 AND toid=12) as unreadsrn
            FROM dt_inbox d
            WHERE (toid = 12 AND inboxdelete=0
            OR fromid = 12 AND inboxdelete=0)
            GROUP BY conversationid
            ORDER BY datemax DESC

This give the following result :

messageid  conversationid  fromid  toid  datemax  messagesnr  unreadsrn
     1239            2139    12     159   date       1             0    
     1238            2138    12      22   date       1             1    
     1237            2137    12     159   date       1             0    
     1236            2136    12      22   date       1             0
     1235            2135    159     12   date       1             1    
     1234            2134    159     12   date       1             1        

In this example for userid=12, I want to have only the message between this user and all others, 一条消息， ，

I want my result as :

messageid  conversationid  user1  user2  direction  datemax  messagesnr  unreadsrn
     1239            2139    12     159   from        date       1           0    
     1238            2138    12      22    to         date       1           1    

the new column "direction" will be a flag showing if the last message if from or to userid=12.

Thanks in advance for your help, i'm really blocked :(

Answer 1

Haven't tried it ;-) But maybe the right way to go.

SELECT max(messageid) as messageid, conversationid, fromid, toid,
       datemax, messagesnr, unreadsrn, toid as tmp_toid
    FROM dt_inbox
    WHERE fromid=12
    GROUP BY toid
JOIN
SELECT max(messageid) as messageid, conversationid, fromid, toid,
       datemax, messagesnr, unreadsrn, fromid as tmp_fromid
    FROM dt_inbox
    WHERE toid=12
    GROUP BY fromid
ON tmp_toid=tmp_fromid