Php 如何使用联接表中的选定项？

如何在变量中存储以下语句的

s.Username

和

r.Username

$stmt = $this->db->prepare('SELECT 
                                  s.Username AS Username1, 
                                  r.Username AS Username2, 
                                  c.time, 
                                  c.message 
                            FROM chatlog c
                            JOIN user s ON (c.source = s.ID)
                            JOIN user r ON (c.receiver = r.ID)
                            WHERE s.ID = :source AND r.ID = :receiver
                                        ');
$stmt->execute(array(':source' => $sender, ':receiver' => $buddyID ));

// I want to store the Source and the Username here..
$row =  $stmt->fetch(PDO::FETCH_ASSOC);
$chatID = $row['Username1'].$row['r.Username2'];

// ..to create a unique logfile here ..
$dummy = fopen($chatID.".html",'w');
fclose($dummy);

// .. and store the log finally in that file which is used to print in the chatbox
while($log = $stmt->fetch(PDO::FETCH_ASSOC))
{
$fp = fopen($chatID.".html", "a");
fwrite($fp, "<div class='chat_msg'>(" . $log['time'] . ")" . $log['name'] .":  " . $log['message'] . "<br />");
fclose($fp);
}

$stmt=$this->db->prepare（'SELECT
s、 用户名为Username1，
r、 用户名为Username2，
c、 时间,，
c、 信息
来自聊天日志c
在上加入用户（c.source=s.ID）
加入用户r ON（c.receiver=r.ID）
其中s.ID=：source和r.ID=：receiver
');
$stmt->execute（数组（':source'=>$sender':receiver'=>$buddyID））；
//我想在这里存储源和用户名。。
$row=$stmt->fetch（PDO:：fetch_ASSOC）；
$chatID=$row['Username1']。$row['r.Username2']；
//…在此处创建唯一的日志文件。。
$dummy=fopen（$chatID..html“，'w'）；
fclose（$虚拟）；
// .. 并最终将日志存储在聊天室中用于打印的文件中
而（$log=$stmt->fetch（PDO:：fetch\U ASSOC））
{
$fp=fopen（$chatID..html，“.a”）；
fwrite（$fp），（“$log['time']”，“$log['name']”：“$log['message']”，“
”；
fclose（$fp）；
}
你是说

SELECT 
       s.Username AS Username1, 
       r.Username AS Username2, 
       c.time, 
       c.message 
FROM chatlog c
JOIN user s ON (c.source = s.ID)
JOIN user r ON (c.receiver = r.ID)
WHERE s.ID = :source AND r.ID = :receiver

你是说

SELECT 
       s.Username AS Username1, 
       r.Username AS Username2, 
       c.time, 
       c.message 
FROM chatlog c
JOIN user s ON (c.source = s.ID)
JOIN user r ON (c.receiver = r.ID)
WHERE s.ID = :source AND r.ID = :receiver