XML XQuery
XQuery is a functional query language purpose-built for extracting, filtering, and reshaping data stored as XML, playing much the same role for XML that SQL plays for relational tables.
#Jobseeker
Find matching jobs & Auto apply with AI
What Is XQuery?
XQuery treats an XML document (or a collection of documents) as a queryable tree and lets you ask questions of it directly: which products cost more than $50, sorted by name? which employees report to a given manager? XQuery is built on top of XPath — every XPath expression is a valid XQuery expression — but it adds the ability to construct new XML output, define reusable functions, and combine data from multiple sources in a single query, which is why it's often described as 'SQL for XML.'
FLWOR Expressions
A Basic FLWOR Query
<!DOCTYPE html>
<html>
<body>
<pre>
for $product in doc("catalog.xml")/catalog/product
where $product/price > 20
order by $product/name
return
<item>
<name>{ $product/name/text() }</name>
<price>{ $product/price/text() }</price>
</item>
</pre>
</body>
</html>FLWOR — pronounced 'flower' — stands for the five clauses that give the expression its shape: for binds a variable to each item in a sequence, let assigns a computed value, where filters the bound items, order by sorts what's left, and return builds the output for every surviving binding. Only for and return are required; let, where, and order by are optional and can be repeated or omitted as the query demands.
Filtering and Joining Two Documents
<!DOCTYPE html>
<html>
<body>
<pre>
for $order in doc("orders.xml")/orders/order
let $cust := doc("customers.xml")/customers/customer[id = $order/customerId]
where $order/total > 100
order by $order/total descending
return
<receipt>
<customer>{ $cust/name/text() }</customer>
<total>{ $order/total/text() }</total>
</receipt>
</pre>
</body>
</html>- for — iterates over a sequence, binding each item in turn to a variable
- let — assigns the result of an expression to a variable without iterating
- where — filters bindings using a boolean condition
- order by — sorts the remaining bindings before output is produced
- return — constructs the XML (or other) output for each surviving binding
- XPath — the path syntax XQuery uses to navigate and select nodes
- Functions — built-in (fn:count, fn:concat, fn:doc) or user-defined with declare function
Writing Functions and Constructing Elements
A Reusable XQuery Function
<!DOCTYPE html>
<html>
<body>
<pre>
declare function local:discounted-price($price as xs:decimal, $percent as xs:decimal) as xs:decimal {
$price - ($price * $percent div 100)
};
for $product in doc("catalog.xml")/catalog/product
return
<product>
<name>{ data($product/name) }</name>
<salePrice>{ local:discounted-price($product/price, 15) }</salePrice>
</product>
</pre>
</body>
</html>Exercise: XML XQuery
What is XQuery primarily designed to do?
