🧾 XQuery Syntax – Structure and Rules for Writing Valid Queries
🧲 Introduction – Why Learn XQuery Syntax?
To write effective and error-free XQuery expressions, you need to understand its syntax structure. XQuery borrows concepts from XPath, SQL, and functional programming, allowing you to select, filter, transform, and output XML data. Mastering XQuery syntax ensures that your queries are not only correct—but also powerful and maintainable.
🎯 In this guide, you’ll learn:
- The basic syntax structure of XQuery
- How expressions are constructed
- Key syntax rules and conventions
- Examples of valid and invalid XQuery code
📄 Basic Structure of an XQuery Script
xquery version "1.0";
(: Optional declaration :)
declare default element namespace "http://example.com/ns";
(: Load XML document :)
for $book in doc("books.xml")//book
where $book/price > 500
order by $book/title
return
<bookInfo>
<title>{$book/title/text()}</title>
<price>{$book/price/text()}</price>
</bookInfo>
✅ This is a complete and valid XQuery FLWOR expression.
🧾 Core Syntax Components
| Component | Description |
|---|---|
xquery version | Declares the version of XQuery used (optional) |
(: comment :) | Block-style comments |
doc("file.xml") | Loads XML document |
for, let | Variables and looping constructs |
where | Filtering condition |
order by | Sorting output |
return | Defines what should be output |
{expression} | Inserts dynamic value in XML/HTML output |
<tag>{...}</tag> | Element constructors for XML or HTML generation |
💡 Syntax Tip: Literal Values
"Hello World" (: string literal :)
123, 456, 789 (: sequence of integers :)
true(), false() (: boolean literals :)
🔠 Variables and Binding
Variables start with $ and are defined using for or let:
let $title := "Learn XQuery"
return <h1>{$title}</h1>
🔍 Conditional Expressions
if ($price > 500) then
<label>Premium</label>
else
<label>Budget</label>
✅ XQuery supports if-then-else for inline conditional logic.
🧮 Arithmetic and Operators
| Operator | Description |
|---|---|
+ | Addition |
- | Subtraction |
* | Multiplication |
div | Division (e.g., 10 div 2) |
mod | Modulo (e.g., 10 mod 3) |
= | Value equality |
!= | Not equal |
<, >, <=, >= | Comparisons |
⚠️ Common Syntax Mistakes
| Mistake | Correction |
|---|---|
Missing return | Always include return in FLWOR |
Forgetting {} around variables | Use <tag>{$var}</tag> not <tag>$var</tag> |
| Unclosed XML elements | All tags must be closed in output |
Using = for node equality | Use is or deep-equals for node comparison |
✅ Best Practices
- ✔️ Use comments
(: ... :)to explain logic - ✔️ Wrap all XPath in
{}when inside XML/HTML tags - ✔️ Indent nested structures for readability
- ✔️ Separate logic into multiple lines for clarity
- ❌ Don’t rely on implicit context—use full paths when needed
📌 Summary – Recap & Next Steps
XQuery syntax is simple but powerful, blending XPath and FLWOR with functional expression handling. Understanding its structure helps you write clean, readable, and efficient queries for transforming and extracting XML data.
🔍 Key Takeaways:
- XQuery uses variables (
$), XPath, and XML constructors - Syntax includes FLWOR, conditionals, and arithmetic
- Use
{}to insert dynamic content inside output elements
⚙️ Real-world relevance: Used in enterprise APIs, e-commerce XML feeds, content management systems, and XML database queries.
❓ FAQs – XQuery Syntax
❓ Is XQuery case-sensitive?
✅ Yes. Tags, functions, and variable names are case-sensitive.
❓ Can XQuery return plain text?
✅ Yes. You can return strings or use <xsl:output method="text"/>.
❓ Do I need to declare xquery version?
❌ Not required, but recommended for clarity.
❓ Can I use comments in XQuery?
✅ Yes. Use (: ... :) to add inline or block comments.
❓ How do I concatenate strings in XQuery?
✅ Use concat("a", "b") or simply "a" || "b" in XQuery 3.0.
Share Now :
