(:
XML Query Use Cases: http://www.w3.org/TR/xquery-use-cases/
Copyright ©2003 World Wide Web Consortium, (Massachusetts Institute of Technology, European Research Consortium for Informatics and Mathematics, Keio University). All Rights Reserved. This work is distributed under the W3C® Software License [1] in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
[1] http://www.w3.org/Consortium/Legal/2002/copyright-software-20021231
:)
(:
 Filename: xmpQ10.xq  
 Source:    http://www.w3.org/TR/xquery-use-cases/#xmp-queries-results-q10  
 Section:   1.1.9.10 Q10  
 Purpose:  In the document "prices.xml", find the minimum price for each book,  in the form of a "minprice" element with the book title as its title attribute. 
 :)

<results>
  {
    let $doc := doc("prices.xml")
    for $t in distinct-values($doc//book/title)
    let $p := $doc//book[title = $t]/price
    return
      <minprice title="{ $t }">
        <price>{ min($p) }</price>
      </minprice>
  }
</results>