CREATE TABLE `student` (
 `id` int(11) NOT NULL auto_increment,
 `name` varchar(50) NOT NULL,
 `sex` varchar(10) NOT NULL,
 `age` smallint(3) NOT NULL default '0',
 PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

include_once ("connect.php"); //连接数据库
$sql = "select * from student";
$result = mysql_query($sql) or die("Invalid query: " . mysql_error());
while ($row = mysql_fetch_array($result)) {
  $arr[] = array(
    'name' => $row['name'],
    'sex' => $row['sex'],
    'age' => $row['age']
  );
}

$doc = new DOMDocument('1.0', 'utf-8'); // 声明版本和编码
$doc->formatOutput = true;
$r = $doc->createElement_x("root");
$doc->appendChild($r);
foreach ($arr as $dat) {
  $b = $doc->createElement_x("data");
  $name = $doc->createElement_x("name");
  $name->appendChild($doc->createTextNode($dat['name']));
  $b->appendChild($name);
  $sex = $doc->createElement_x("sex");
  $sex->appendChild($doc->createTextNode($dat['sex']));
  $b->appendChild($sex);
  $age = $doc->createElement_x("age");
  $age->appendChild($doc->createTextNode($dat['age']));
  $b->appendChild($age);
  $r->appendChild($b);
}
echo $doc->saveXML();

<?xml version="1.0" encoding="utf-8"?>
<root>
 <data>
  <name>李王皓</name>
  <sex>男</sex>
  <age>21</age>
 </data>
 ...
</root>

header("Content-type:text/html; Charset=utf-8");
$url = "http://www.helloweba.com/demo/importXML/createXML.php";
$reader = new XMLReader(); //实例化XMLReader
$reader->open($url); //获取xml
$i=1;
while ($reader->read()) {
 if ($reader->nodeType == XMLReader::TEXT) { //判断node类型
   $m = $i%3;
   if($m==1)
     $name = $reader->value; //读取node值
   if($m==2)
     $sex = $reader->value;
   if($m==0){
     $age = $reader->value;
     $arr[] = array(
       'name' => $name,
       'sex' => $sex,
       'age' => $age
     );
   }
   $i++;
 }
}
//print_r($arr);