php - 选择 *，最后(日期时间)

Question

我正在运行一个 while 循环来获取每个对话的最新消息，但是我收到了错误

[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

这是完整的循环。它在我添加 ,LAST(date_time) 和 GROUP BY 对话之前起作用但是我只想在每个对话中显示最新消息，而不是每条消息。我该怎么做？

<?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 } ?>

谢谢。

Answer 1

GROUP BY 子句在 WHERE 之后，ORDER BY 子句之前:

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