php如何逐行写txt文件？

[kaixinmaitian]

用数据库循环后得到字符串后一次性写txt文件，由于循环量过大，所以想循环一条写一条到txt文件未尾的代码应该如何写？下面的代码应该如何改？

<?php
require_once("conn.php");
$query = "SELECT * FROM news order by id desc";
$result = mysql_query($query) or die("Query failed : " . mysql_error());
while ($row=mysql_fetch_array($result)) {
$url="http://www.xxx.com/thread-".$row['id'].".html\r\n";
$path="sitemap.txt";
$handle=fopen($path,"w");
fwrite($handle,$url);
fclose($handle);
}
mysql_free_result($result);
?>

[嘻哈大咖秀]

$handle=fopen($path,"a+");