Question

Im developing a chat tool and im having problems with the sql returning the right results with group by and order by. The table has a structure shown below;

tablename: chat

id | from | to | sent | read | message

‘from’ and ‘to’ are a signed integers (userids)
‘sent’ is a timestamp when the message was sent.
‘message’ is text msg
‘read’ is an int (0 for unread, 1 for read).

im trying to return a list of the most recent messages grouped by users

eg

id         from     to      message        sent    read
7324       21      1       try again    1349697192  1
7325       251       1     yo whats up  1349741502  0
7326       251       1     u there      1349741686  0   

should return this after the query

    id      from    to     message      sent        read
7326        251     1        u there    1349741686   0
7324        21      1       try again    1349697192  1

here is my query

$q ="SELECT chat.to,chat.read,chat.message,chat.sent,chat.from FROM `chat` WHERE chat.to=$userid GROUP BY chat.from ORDER BY chat.sent DESC,chat.read ASC LIMIT ".(($page-1)*$count).",$count";            

it doesnt return the desired results;

Answer 1

You should create a subquery which determines the latest sent by users then join it with chat table.

SELECT  a.*                   -- this will list all latest rows from chat table
FROM    `chat` a
        INNER JOIN
        (
            SELECT `from`, `to`, MAX(sent) maxSent
            FROM `chat`
            GROUP BY `from`, `to`
        ) b ON a.`from` = b.`from` AND
                a.`to` = b.`to` AND
                a.sent = b.maxSent
-- WHERE ....                 -- add your condition(s) here

SQLFiddle Demo