XQuery - FLWOR


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FLWOR is an acronym that stands for "For, Let, Where, Order by, Return". The following list shows what they account for in a FLWOR expression −

  • F - For - Selects a collection of all nodes.

  • L - Let - Puts the result in an XQuery variable.

  • W - Where - Selects the nodes specified by the condition.

  • O - Order by - Orders the nodes specified as per criteria.

  • R - Return - Returns the final result.

Example

Following is a sample XML document that contains information on a collection of books. We will use a FLWOR expression to retrieve the titles of those books with a price greater than 30.

books.xml

<?xml version="1.0" encoding="UTF-8"?>
<books>
   
   <book category="JAVA">
      <title lang="en">Learn Java in 24 Hours</title>
      <author>Robert</author>
      <year>2005</year>
      <price>30.00</price>
   </book>
   
   <book category="DOTNET">
      <title lang="en">Learn .Net in 24 hours</title>
      <author>Peter</author>
      <year>2011</year>
      <price>70.50</price>
   </book>
   
   <book category="XML">
      <title lang="en">Learn XQuery in 24 hours</title>
      <author>Robert</author>
      <author>Peter</author> 
      <year>2013</year>
      <price>50.00</price>
   </book>
   
   <book category="XML">
      <title lang="en">Learn XPath in 24 hours</title>
      <author>Jay Ban</author>
      <year>2010</year>
      <price>16.50</price>
   </book>
   
</books>

The following Xquery document contains the query expression to be executed on the above XML document.

books.xqy

let $books := (doc("books.xml")/books/book)
return <results>
{
   for $x in $books
   where $x/price>30
   order by $x/price
   return $x/title
}
</results>

Result

<title lang="en">Learn XQuery in 24 hours</title>
<title lang="en">Learn .Net in 24 hours</title>

Verify Result

To verify the result, replace the contents of books.xqy (given in theEnvironment Setup chapter) with the above XQuery expression and execute the XQueryTester java program.



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