XQuery FLWR Expressions

Expression:

Example(s):

FLWR Expressions

1. <root>

   {

     FOR $a IN document("xqt")//tutorials

     RETURN $a/tutorial/title

   }

   </root>

This xquery returns the following:

<?xml version="1.0"?>

<root>

  <title>Introduction to XQuery</title>

  <title>XQuery's Syntax</title>

  <title>XQuery: Advanced Tricks</title>

</root>

This xquery is exactly the same as the second example in the Path Expression example section above. This time however, we can use the FLWR Expression type to create very powerful xqueries. Let's look at a second example to see how.

A common way to nest FLWR Expressions is to include a new FLWR expression after the RETURN keyword; an example that builds on the previous example is as follows:

2. <root>

   {

     FOR $a IN document("xqt")//tutorials

     RETURN

     <tutorial>

     {

       FOR $b IN document("xqt")//tutorials

       WHERE $a = $b

       RETURN $b/tutorial/id

     }

     </tutorial>

   }

   </root>

Although we do not have a second document (navigator) available (only "xqt" is present in the navigator collection), this xquery shows how we could produce a UNION of two or more different tables, using XQuery. The xquery produces the following output:

<?xml version="1.0"?>

<root>

  <tutorial>

    <id>T000001</id>

    <id>T000002</id>

    <id>T000003</id>

  </tutorial>

</root>