XQuery Syntax and Expressions

Estimated study time: 14 minutes.

Most real-world XQuery code is built around the FLWOR expression — a structured pattern named after its five clauses: For, Let, Where, Order by, Return.

For Clause

for $course in doc("courses.xml")//course
return $course/title

Iterates over each matching node, similar to a loop.

Let Clause

let $allCourses := doc("courses.xml")//course
return count($allCourses)

Binds a variable to a value or a node set, without iterating.

Where Clause

for $course in doc("courses.xml")//course
where $course/@level = "beginner"
return $course/title

Filters the results, just like SQL's WHERE.

Order By Clause

for $course in doc("courses.xml")//course
order by $course/title
return $course/title

Sorts the returned results.

Constructing New XML

for $course in doc("courses.xml")//course
return <summary>{$course/title/text()}</summary>

XQuery lets you build brand-new XML elements directly inside the query, embedding selected values with curly braces.