Question

I’m running a while loop to get the most recent message of each conversation, however I am getting the error

[18-Feb-2012 21:14:59] PHP Warning:  mysql_fetch_array(): supplied argument is not a valid MySQL result resource in /path/messages.php on line 44

Here is the full loop. It worked before I added ,LAST(date_time) and GROUP BY conversation however I only want to display the latest message in each conversation, not every single message. How can I do this?

<?php 
  $current_user = user_info('id',1); //get logged in user id
  $query = mysql_query("SELECT *, LAST(date_time) 
                          FROM messages 
                         WHERE user_to='$current_user' 
                      ORDER BY date_time DESC 
                         LIMIT 0,5 
                      GROUP BY conversation");
  while($message = mysql_fetch_array($query)) { 
?>
                <li><strong><?php user_info('first_name',0,$message['user_from']); ?> <?php $sender_last_name = user_info('last_name',0,$message['user_from']); ?></strong><span class="message_time"><?php echo time2str($message['date_time']); ?></span><br />
                <span class="message_description"><?php echo substr($message['content'],0,50); ?></span></li>
                <?php } ?>

Thanks.

Answer 1

The GROUP BY clause goes after the WHERE, before the ORDER BY clause:

  $query = mysql_query("SELECT *, LAST(date_time) 
                          FROM messages 
                         WHERE user_to='$current_user' 
                      GROUP BY conversation
                      ORDER BY date_time DESC 
                         LIMIT 0,5 ");