problemas con inner join

[enlinea777]

prueba esto

Código PHP:

$sql1 = "SELECT * FROM REGISTER_USERS WHERE USERNAME='$username'";
        $result1 = mysql_query($sql1) or die(mysql_error());
        
        $fila1 = mysql_fetch_assoc($result1);
        
        $sql = "SELECT * FROM REGISTER_USERS r INNER JOIN AVATARS a ON r.IUID = a.IUID WHERE r.IUID = '".$fila1['IUID']."'";
        $result = mysql_query($sql) or die(mysql_error());
        
        while($fila = mysql_fetch_assoc($resultado)) {
            $_SESSION['login'] = true;
            $_SESSION['avatar'] = $fila['IMAGE'];
            $_SESSION['username'] = $fila['USERNAME'];
            $_SESSION['upload'] = $fila['UPLOADS'];
        }