Using XQUERY FLWOR

How to use FLWOR to extract an XML segment from an XML document.

XQuery's FLWOR expression allows you to construct queries that can manipulate and return XML data efficiently. FLWOR stands for For, Let, Where, Order by, and Return. Here’s a breakdown of how it works:

Basic Structure of FLWOR

for $variable in $sequence
let $anotherVariable := expression
where condition
order by $sortExpression
return expression

Components

1. For: Iterates over a sequence.
2. Let: Binds a variable to a value.
3. Where: Filters the results based on a condition.
4. Order by: Sorts the results.
5. Return: Specifies what is returned as the output.

Example

Here’s a simple example that demonstrates the use of FLWOR to query an XML document:

declare namespace ex = "http://example.com";

let $xml := 
<books>
  <book>
    <title>Learning XQuery</title>
    <author>John Doe</author>
    <price>29.99</price>
  </book>
  <book>
    <title>Advanced XQuery</title>
    <author>Jane Smith</author>
    <price>39.99</price>
  </book>
</books>

for $book in $xml/book
where $book/price > 30
order by $book/title
return <result>
         <title>{$book/title/text()}</title>
         <author>{$book/author/text()}</author>
       </result>

Explanation

• Let: Initializes the $xml variable with a sample XML structure.
• For: Iterates over each <book> element.
• Where: Filters books with a price greater than 30.
• Order by: Sorts the results by the title of the book.
• Return: Constructs a new XML element for each filtered book.

Conclusion

FLWOR expressions provide a powerful way to query and manipulate XML data, making it a key feature in XQuery. If you have specific queries or scenarios you want to explore, feel free to ask!