拆分序列

Question

我刚刚开始使用 xQuery 作为数据库课程的一部分。对于课程，我们使用的是此处的 mondial 数据库 (https://www.dbis.informatik.uni-goettingen.de/Mondial/)。基本上，该数据库包含有关世界、国家、湖泊、河流等的信息。

我们的一项任务是获取所有拥有岛屿的湖泊的面积，然后按大陆对其进行分组。到目前为止，我已经这样做了：

let $lakes := 
    for $lakeList in doc("mondial.xml")/mondial/lake[@island]
      for $country in doc("mondial.xml")/mondial/country

      where $lakeList/located/@country = $country/@car_code

  return <lake area = "{$lakeList/area}" country = "{$country/name}" continent = "{$country/encompassed/@continent}" continentPerc = "{$country/encompassed/@percentage}"></lake> 

return ($lakes)

这个查询会产生以下结果：

<lake area="40.2" country="Denmark" continent="europe" continentPerc="100"/>
<lake area="56" country="United Kingdom" continent="europe" continentPerc="100"/>
<lake area="71" country="United Kingdom" continent="europe" continentPerc="100"/>
<lake area="10" country="Russia" continent="europe asia" continentPerc="25 75"/>
<lake area="670" country="Japan" continent="asia" continentPerc="100"/>
<lake area="1.8" country="Philippines" continent="asia" continentPerc="100"/>
<lake area="234.2" country="Philippines" continent="asia" continentPerc="100"/>
<lake area="0.3" country="Philippines" continent="asia" continentPerc="100"/>
<lake area="911" country="Philippines" continent="asia" continentPerc="100"/>
<lake area="354.6" country="Philippines" continent="asia" continentPerc="100"/>
<lake area="1103" country="Indonesia" continent="asia australia" continentPerc="78 22"/>
<lake area="0.04" country="Indonesia" continent="asia australia" continentPerc="78 22"/>
<lake area="11.3" country="Indonesia" continent="asia australia" continentPerc="78 22"/>
<lake area="537.5" country="Canada" continent="america" continentPerc="100"/>
<lake area="5542" country="Canada" continent="america" continentPerc="100"/>
<lake area="104" country="Canada" continent="america" continentPerc="100"/>
<lake area="38.7" country="Canada" continent="america" continentPerc="100"/>

现在求和的问题似乎是某些属性包含多个值。所以不可能按大陆分组。因此，我想拆分具有多个 continent 和 continentPerc 的序列，以便该区域对应于各自的大陆。

我的意思示例：

<lake area="1103" country="Indonesia" continent="asia australia" continentPerc="78 22"/>

应该变成

<lake area="1103" country="Indonesia" continent="asia" continentPerc="78"/>

<lake area="1103" country="Indonesia" continent="australia" continentPerc="22"/>

这可以通过某种方式实现还是我应该选择其他策略？

我非常感谢我能得到的任何帮助和指点，因为我不擅长 Xquery。提前致谢。

Answer 1

我不熟悉那个数据库结构，我不确定我是否理解了这个问题（仍然想知道一个湖是否可以属于亚洲和澳大利亚）但是如果你直接提取大陆并将元组流分组到大陆，如在

let $countries := doc('mondial.xml')/mondial/country
for $lake in doc("mondial.xml")/mondial/lake[@island]
for $continent in $countries[@car_code = tokenize($lake/@country, '\s+')]/encompassed/@continent
group by $continent
order by $continent
return <continent name="{$continent}">{$lake/<lake name="{@id}" area="{area}"/>}</continent>

然后你得到

<continent name="america">
   <lake name="lake-Hazen" area="537.5"/>
   <lake name="lake-Nettilling" area="5542"/>
   <lake name="lake-Lake_Manitou" area="104"/>
   <lake name="lake-Mindemoya" area="38.7"/>
</continent>
<continent name="asia">
   <lake name="lake-KoltsevoyeLake" area="10"/>
   <lake name="lake-Biwa" area="670"/>
   <lake name="lake-Pinatubo" area="1.8"/>
   <lake name="lake-Taal" area="234.2"/>
   <lake name="lake-TaalCrater" area="0.3"/>
   <lake name="lake-LagunaDeBay" area="911"/>
   <lake name="lake-Lanao" area="354.6"/>
   <lake name="lake-Toba" area="1103"/>
   <lake name="lake-DanauKumbang" area="0.04"/>
   <lake name="lake-SegaraAnak" area="11.3"/>
</continent>
<continent name="australia">
   <lake name="lake-Toba" area="1103"/>
   <lake name="lake-DanauKumbang" area="0.04"/>
   <lake name="lake-SegaraAnak" area="11.3"/>
   <lake name="lake-LakeTaupo" area="622"/>
   <lake name="lake-Wanaka" area="192"/>
</continent>
<continent name="europe">
   <lake name="lake-Arresoe" area="40.2"/>
   <lake name="lake-LoughNeagh" area="392"/>
   <lake name="lake-LochNess" area="56"/>
   <lake name="lake-LochLomond" area="71"/>
   <lake name="lake-KoltsevoyeLake" area="10"/>
</continent>

尝试合并我提出的国家和百分比数据

let $countries := doc('mondial.xml')/mondial/country
for $lake in doc("mondial.xml")/mondial/lake[@island]
for $lake-country in $countries[@car_code = $lake/located/@country]
for $continent in $lake-country/encompassed
group by $continent-name := $continent/@continent
order by $continent-name
return 
  <continent name="{$continent-name}">{
     $lake!<lake name="{@id}"
                        area="{area}"
                        country="{let $l := . return $countries[@car_code = $l/located/@country and encompassed[@continent = $continent-name]]/name}"
                        percentage="{let $l := . return $countries[@car_code = $l/located/@country]/encompassed[@continent = $continent-name]/@percentage}"/>
    }</continent>

我希望有更优雅和紧凑的方式来表达它，但它似乎可以完成这项工作。