PHP将数据从mysql数据库输出到XML文件

我正在将mysql数据库中的数据转换成XML文件。我使用下面的PHP代码来获得输出

PHP代码：

<?php

mysql_connect('localhost', 'root', '');
mysql_select_db('emptestdb');

$sql = "SELECT  name, username, DATE(visitdate) AS vdate, DATE(retdate) AS rdate, location FROM users";
$res = mysql_query($sql);

header("Content-Type: text/html/force-download");
header("Content-Disposition: attachment; filename='EMP_RECORDS.xml'");

$xml = new XMLWriter();

$xml->openURI("php://output");
$xml->startDocument('1.0','UTF-8');
$xml->setIndent(true);

$xml->startElement('engineers');

while ($row = mysql_fetch_assoc($res)) {
  $xml->startElement("engineer");

  $xml->writeAttribute('engID', $row['username']);
  $xml->writeAttribute('engName', $row['name']);

  $xml->startElement("location");
  $xml->writeAttribute('fieldLoc', $row['location']);

  $xml->writeElement('vistiDate',$row['vdate']);
  $xml->writeElement('retDate',$row['rdate']);

  $xml->endElement();
  $xml->endElement();
}

$xml->endElement();

header('Content-type: text/xml');

$xml->flush();
?>

在使用上述代码时，我得到了以下XML输出

目前产出：

<?xml version="1.0" encoding="UTF-8"?>

    <engineers>
     <engineer engID="1" engName="John">
      <location fieldLoc="Geneva">
       <vistiDate>2015-01-23</vistiDate>
       <retDate>2015-06-28</retDate>
      </location>
     </engineer>
     <engineer engID="1" engName="John">
      <location fieldLoc="Paris">
       <vistiDate>2015-02-12</vistiDate>
       <retDate>2015-02-17</retDate>
      </location>
     </engineer>
     <engineer engID="2" engName="Josh">
      <location fieldLoc="Paris">
       <vistiDate>2015-02-12</vistiDate>
       <retDate>2015-02-17</retDate>
      </location>
     </engineer>
    <engineer engID="3" engName="Rita">
      <location fieldLoc="Paris">
       <vistiDate>2015-02-12</vistiDate>
       <retDate>2015-02-17</retDate>
      </location>
     </engineer>
    </engineers>

2015-01-23
2015-06-28
2015-02-12
2015-02-17
2015-02-12
2015-02-17
2015-02-12
2015-02-17

我正在尝试对engID进行分组，并获得以下输出

期望输出：

<?xml version="1.0" encoding="UTF-8"?>
<engineers>
 <engineer engID="1" engName="John">
  <location fieldLoc="Geneva">
   <vistiDate>2015-01-23</vistiDate>
   <retDate>2015-06-28</retDate>
  </location>

  <location fieldLoc="Paris">
   <vistiDate>2015-02-12</vistiDate>
   <retDate>2015-02-17</retDate>
  </location>
</engineer>

 <engineer engID="2" engName="Josh">
  <location fieldLoc="Paris">
   <vistiDate>2015-02-12</vistiDate>
   <retDate>2015-02-17</retDate>
  </location>
 </engineer>

 <engineer engID="3" engName="Rita">
  <location fieldLoc="Paris">
   <vistiDate>2015-02-12</vistiDate>
   <retDate>2015-02-17</retDate>
  </location>
 </engineer>
</engineers>

2015-01-23
2015-06-28
2015-02-12
2015-02-17
2015-02-12
2015-02-17
2015-02-12
2015-02-17

有人能指导我如何把它组合在一起吗。 谢谢。

一个不错的主意应该是

处理数据并保存它

生成xml

$engineers = [];
// process data
while ($row = mysql_fetch_assoc($res)) {
     if (!isset($engineers[$row['username']])) {
         $engineers[$row['username']] = [
              'name'      => $row['name'],
              'locations' => [],
         ];
     }
     $engineers[$row['username']]['locations'][] = [
     $xml->writeAttribute('fieldLoc', $row['location']);
       'vistiDate' => $row['vdate'],
       'retDate'   => $row['rdate']);
     ];
}
// generate xml

foreach ($engineers as $engineer) {
     // add engineer info to xml
     foreach ($engineer['locations'] as $location) {
          // add location to xml
     }
}

一个不那么坏的主意应该是

处理数据并保存它

生成xml

$engineers = [];
// process data
while ($row = mysql_fetch_assoc($res)) {
     if (!isset($engineers[$row['username']])) {
         $engineers[$row['username']] = [
              'name'      => $row['name'],
              'locations' => [],
         ];
     }
     $engineers[$row['username']]['locations'][] = [
     $xml->writeAttribute('fieldLoc', $row['location']);
       'vistiDate' => $row['vdate'],
       'retDate'   => $row['rdate']);
     ];
}
// generate xml

foreach ($engineers as $engineer) {
     // add engineer info to xml
     foreach ($engineer['locations'] as $location) {
          // add location to xml
     }
}