Query with distinct

For each author in the bibliography, list the author's name and the titles of all books by that author, grouped inside a result element.

<results>
   FOR $a IN distinct(document("http://www.bn.com")//author)
   RETURN
    <result>
     $a,
     FOR $b IN document("http://www.bn.com")/bib/book[author=$a]
     RETURN $b/title
    </result>
</results>

Adapted from XML Query Use Cases