XQuery中的全局变量，不知道如何返回平均值，也不知道为什么会出现这个错误

Question

我已经处理第二个简单查询好几天了。我所要做的就是声明一个全局变量（$crimes），该变量指向XML文件中的所有crime元素，并使用FLWOR查询迭代day元素的每个唯一值，这样我就可以看到哪些日子的crime最多（按顺序应该是周六、周一，然后是周日）。我也不断得到这个错误：

查询意外结束；变量"$犯罪"。

代码：

    xquery version "1.0";
delare variable $crimes := doc('dc_crime.xml')//crime;
(: 
   Query to display total number of crimes by
   day of the week
 :)
<results>{
    for $day in distinct-values(doc('dc_crime.xml')/$day
    let $crimes := sum($crimes/($day/$crimes))
    order by $day descending order
    return
    <crime day="{$day}" crimes="{$count}">{$crimes}</crime>
}</results>

XML示例：

       <crime id="13402531">
      <dateTime>2013-08-31T20:27:00</dateTime>
      <month>8-Aug</month>
      <day>7-Sat</day>
      <offense>THEFT/OTHER</offense>
      <method>OTHERS</method>
      <ward>3</ward>
   </crime>
   <crime id="13402533">
      <dateTime>2013-08-28T17:06:00</dateTime>
      <month>8-Aug</month>
      <day>4-Wed</day>
      <offense>THEFT F/AUTO</offense>
      <method>OTHERS</method>
      <ward>1</ward>
   </crime>
   <crime id="13402547">
      <dateTime>2013-08-31T20:05:00</dateTime>
      <month>8-Aug</month>
      <day>7-Sat</day>
      <offense>THEFT F/AUTO</offense>
      <method>OTHERS</method>
      <ward>6</ward>
   </crime>
   <crime id="13402704">
      <dateTime>2013-08-03T17:29:00</dateTime>
      <month>8-Aug</month>
      <day>7-Sat</day>
      <offense>THEFT/OTHER</offense>
      <method>OTHERS</method>
      <ward>2</ward>
   </crime>
</crimes>

请帮忙。。。

Answer 1

这是一个可能的XQuery，它：1。使用全局变量，2。计算每天的犯罪数量，并按该数字的顺序返回结果，降序为：

declare variable $crimes := doc('dc_crime.xml')//crime;
<results>{
    for $day in distinct-values(doc('dc_crime.xml')//day)
    (: get all crimes that happen at current day of week :)
    let $details := $crimes[day=$day] 
    (: count number crimes that happen at current day of week :)
    let $count := count($details)
    (: return the result in the order of $count, descending :)
    order by $count descending
    return
    <crime day="{$day}" crimes="{$count}">{$details}</crime>
}</results>

xpathtester demo

输出：

<results>
   <crime crimes="3" day="7-Sat">
      <crime id="13402531"> 
         <dateTime>2013-08-31T20:27:00</dateTime>  
         <month>8-Aug</month>  
         <day>7-Sat</day>  
         <offense>THEFT/OTHER</offense>  
         <method>OTHERS</method>  
         <ward>3</ward> 
      </crime>
      <crime id="13402547"> 
         <dateTime>2013-08-31T20:05:00</dateTime>  
         <month>8-Aug</month>  
         <day>7-Sat</day>  
         <offense>THEFT F/AUTO</offense>  
         <method>OTHERS</method>  
         <ward>6</ward> 
      </crime>
      <crime id="13402704"> 
         <dateTime>2013-08-03T17:29:00</dateTime>  
         <month>8-Aug</month>  
         <day>7-Sat</day>  
         <offense>THEFT/OTHER</offense>  
         <method>OTHERS</method>  
         <ward>2</ward> 
      </crime>
   </crime>
   <crime crimes="1" day="4-Wed">
      <crime id="13402533"> 
         <dateTime>2013-08-28T17:06:00</dateTime>  
         <month>8-Aug</month>  
         <day>4-Wed</day>  
         <offense>THEFT F/AUTO</offense>  
         <method>OTHERS</method>  
         <ward>1</ward> 
      </crime>
   </crime>
</results>