Xquery fn:min功能不工作

好的，我有一个xml：

<?xml version="1.0" encoding="UTF-8" ?>
<dvdCollection xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://teste1.org"
xsi:noNamespaceSchemaLocation="http://teste1.org dvds.xsd">
<dvd>
<id>1</id>
<title>Pulp Fiction</title>
<release-year>1994</release-year>
<director>Quentin Tarantino</director>
<actors>
< actor type="star" gender="male">John Travolta</actor>
<actor type="star" gender="female">Uma Thurman</actor>
<actor type="co-star" gender="male">Samuel L. Jackson</actor>
</actors>
<genres><genre>Crime</genre><genre>Drama</genre></genres>
</dvd>
<dvd>
<id>2</id>
<title>Green mile</title>
<release-year>1993</release-year>
<director>Quentin Tarantino</director>
<actors>
<actor type="star" gender="male">Tom hanks</actor>
</actors>
<genres><genre>Crime</genre></genres>
</dvd>
<dvd>
<id>3</id>
<title>Titanic</title>
<release-year>1999</release-year>
<director>Quentin Tarantino</director>
<actors>
<actor type="star" gender="male">Tom hanks</actor>
</actors>
<genres><genre>Crime</genre></genres>
</dvd>
</dvdCollection>

---

提前谢谢

对于每个有类似错误的人： 好的，那么fn:min做了我认为应该做的事情，问题是因为for指令，我对每个元素应用了fn:min。这不是我想要的，我想把一系列的发布年份分组，所以我需要做的事情非常简单

declare default element namespace "http://teste1.org";
let $dvds := fn:doc("dvdcollection.xml")//dvd
**let** $dvd := $dvds//genre[.="Crime"]
let $min := fn:min($dvd/../../release-year)
return $min

只要将“for”替换为“let”，错误就被清除了

    declare default element namespace "http://teste1.org";
    let $dvds := fn:doc("dvdcollection.xml")//dvd
    for $dvd in $dvds//genre[.="Crime"]
    let $min := fn:min($dvd/../../release-year)
    return $min

declare default element namespace "http://teste1.org";
let $dvds := fn:doc("dvdcollection.xml")//dvd
**let** $dvd := $dvds//genre[.="Crime"]
let $min := fn:min($dvd/../../release-year)
return $min