在xml中查找每个元素属性的最大值？

在过去的一个小时里，我一直在寻找如何找到按元素分组的最大值，但没有成功

我试图报告每个用户播放次数最高的播放列表的pid、uid和播放次数

这是我的xml文件：

<!DOCTYPE users SYSTEM "users.dtd">
<users>
 <user uid = "u1" dob = "06/03/94" email = "tom@hotmail.com">
    <surname> Doe</surname>
    <givennames> Jon </givennames>
    <follows who = "u1 u2"/>
    <playlists>
      <playlist pid = "p1" created ="12/03/11" playcount = "5" /> 
    </playlists>
   </user>

  <user uid = "u2" dob = "06/03/95" email = "jane@hotmail.com">
    <surname> Dod</surname>
    <givennames> Jane </givennames>
    <follows who = "u1 u3"/>
   </user>

   <user uid = "u3" dob = "06/04/95" email = "dave@hotmail.com">
    <surname> ron</surname>
    <givennames> dave </givennames>
    <follows who = "u1 u2"/>
    <playlists>
      <playlist pid = "p3" created ="12/02/09" playcount = "9"/> 
      <playlist pid = "p9" created = "11/11/11" playcount = "11"/>
     </playlists>
   </user>

   <user uid = "u4" dob = "06/04/99" email = "jeff@hotmail.com">
    <surname> dun</surname>
    <givennames> jeff</givennames>
     <follows who = "u1 u2 u3"/>
    <playlists>
      <playlist pid = "p4" created ="12/02/09" playcount = "3"/> 
      <playlist pid = "p6" created ="12/02/09" playcount = "55"/>
    </playlists>
   </user>

</users>

但它不起作用。我尝试过的任何东西都不起作用。它要么返回每个用户的最大播放次数（这是我得到的最好结果，因为这有点像我想从这个查询中得到什么），要么我得到每个播放列表

我需要一个输出以下内容的查询：

<favorites>
   <user uid = "u1" pid = "p1" playcount = "5"/>
   <user uid = "u2" />
   <user uid = "u3" pid = "p9" playcount = "11"/>
   <user uid = "u4" pid = "p6" playcount = "55"/>
</favorites>

播放列表是可选元素，因此如果用户没有播放列表，则只需报告uid即可

---

有什么帮助吗？在这里我真是束手无策，因为似乎很难找到一个使用按元素分组的max函数来查找查询的示例。

我想您需要对案例进行分支，并自定义输出格式。这是我的xquery：

let $users := doc("users.xml")/users/user
for $user in $users
let $maxCount := max($user/playlists/playlist/@playcount)
let $maxPlaylist := $user/playlists/playlist[@playcount = $maxCount]
return if (count($maxPlaylist) > 0)
then <user uid="{$user/@uid}" pid = "{$maxPlaylist/@pid}" playcount = "{$maxPlaylist/@playcount}"/>
else <user uid="{$user/@uid}"/>

let$users:=doc（“users.xml”）/users/user
$user中的$user
让$maxCount:=max（$user/playlists/playlist/@playcount）
让$maxPlaylist:=$user/playlists/playlist[@playcount=$maxCount]
如果（计数（$maxPlaylist）>0，则返回
然后
其他的

XQuery 1.0还是XQuery 3.0？版本3.0有一个“分组依据”结构。

let $users := doc("users.xml")/users/user
for $user in $users
let $maxCount := max($user/playlists/playlist/@playcount)
let $maxPlaylist := $user/playlists/playlist[@playcount = $maxCount]
return if (count($maxPlaylist) > 0)
then <user uid="{$user/@uid}" pid = "{$maxPlaylist/@pid}" playcount = "{$maxPlaylist/@playcount}"/>
else <user uid="{$user/@uid}"/>