IF THEN ELSE

Query: For each book that has at least one author, list the title and first two authors, and an empty "et-al" element if the book has additional authors

<bib>
   FOR $b IN document("http://www.bn.com/bib.xml")//book
   WHERE count($b/author) > 0
   RETURN
    <book>
     $b/title,
     FOR $a IN $b/author[RANGE 1 TO 2] RETURN $a,
     IF count($b/author) > 2 THEN <et-al/> ELSE [ ]
    </book>
</bib>

Adapted from XML Query Use Cases