MarkLogic: XQuery to Get Distinct Names from XML Document?

Question

I am using the following file:

<bookstore>
  <book category="COOKING">
    <title lang="en">Everyday Italian</title>
    <author>Giada De Laurentiis</author>
    <year>2005</year>
    <price>30.00</price>
  </book>
  <book category="CHILDREN">
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
  <book category="WEB">
    <title lang="en">XQuery Kick Start</title>
    <author>James McGovern</author>
    <author>Per Bothner</author>
    <author>Kurt Cagle</author>
    <author>James Linn</author>
    <author>Vaidyanathan Nagarajan</author>
    <year>2003</year>
    <price>49.99</price>
  </book>
  <book category="WEB">
    <title lang="en">Learning XML</title>
    <author>Erik T. Ray</author>
    <year>2003</year>
    <price>39.95</price>
  </book>
</bookstore>

I am using the following query to get the names from the XML document

for $x at $i in doc("bookstore.xml")/bookstore/book/*
return fn:distinct-values(name($x))

I am getting following results:

title
author
year
price
title
author
year
price
title
author
author
author
author
author
year
price
title
author
year
price

Instead I just want the distinct one as shown below.

title
author
year
price

I believe I messed up the for loop. Can someone help me with a fix for this? I tried using distinct-values(). No luck.

Answer 1

name($x) contains name of element that currently referenced by variable $x. And $x always references one element at a time, so calling distinct-values() on name($x) won't be useful. Instead, you want to call distinct-values() on a collection containing all the elements name, like for example :

let $result := 
    for $x at $i in doc("bookstore.xml")/bookstore/book/*
    return name($x)
return fn:distinct-values($result)

This can also be achieved using plain XPath expression as follow :

distinct-values(doc("bookstore.xml")/bookstore/book/*/name(.))