結合されたテーブルから選択したアイテムを使用するには？

Question

次の文のs.Usernameとr.Usernameを変数にどのように格納できますか？あなたは

$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); 
} 

Answer 1

を意味していますか？

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