XQuery Syntax

⚙️ What is XQuery Syntax?

XQuery syntax defines the rules for writing valid XQuery expressions. It combines path expressions, FLWOR statements, and functions to query and transform XML data with clear, readable code structure.


(: Basic XQuery syntax :)
for $item in //product
where $item/@price < 50
return $item/name

Basic Syntax Rules

XQuery follows specific syntax rules that make queries readable and maintainable. Understanding these rules is essential for writing correct XQuery expressions.

💬

Comments

Document your code

(: This is a comment :)

💲

Variables

Start with $ symbol

let $x := 10

📏

Case Sensitive

Names are case-sensitive

$name ≠ $Name

🔤

Strings

Use quotes for text

"Hello" or 'World'

🔹 Path Expression Syntax

Path expressions navigate through XML structure:

(: Absolute path :)
/bookstore/book/title

(: Relative path :)
book/title

(: Descendant path :)
//title

(: With predicate :)
//book[@category="fiction"]/title

/ - Selects from root or direct children
// - Selects descendants at any level
@ - Selects attributes
[ ] - Filters with predicates

🔹 FLWOR Expression Syntax

FLWOR is the most powerful XQuery construct:

(: Complete FLWOR example :)
for $book in //book
let $discount := $book/@price * 0.1
where $book/@price > 20
order by $book/title
return 
  <discounted>
    {$book/title}
    <newPrice>{$book/@price - $discount}</newPrice>
  </discounted>

for: Iterates through sequences
let: Binds variables to values
where: Filters results
order by: Sorts results
return: Specifies output

🔹 Conditional Syntax

Use if-then-else for conditional logic:

(: Simple condition :)
if ($price < 20) 
then "Cheap"
else "Expensive"

(: In FLWOR :)
for $book in //book
return
  if ($book/@price < 30)
  then <affordable>{$book/title}</affordable>
  else <premium>{$book/title}</premium>

🔹 Comparison Operators

XQuery provides operators for comparisons:

(: Value comparisons :)
$x eq $y    (: equal :)
$x ne $y    (: not equal :)
$x lt $y    (: less than :)
$x le $y    (: less than or equal :)
$x gt $y    (: greater than :)
$x ge $y    (: greater than or equal :)

(: General comparisons :)
$x = $y
$x != $y
$x < $y
$x > $y

🔹 Constructing XML

Create new XML elements in results:

(: Direct constructor :)
<book>
  <title>XQuery Basics</title>
  <author>Jane Smith</author>
</book>

(: Computed constructor :)
element book {
  element title {"XQuery Basics"},
  element author {"Jane Smith"}
}

(: With variables :)
let $title := "XQuery Basics"
return <book><title>{$title}</title></book>

🔹 Arithmetic Operators

Perform calculations in XQuery:

(: Basic arithmetic :)
let $price := 100
let $tax := $price * 0.08
let $total := $price + $tax
return $total

(: Result: 108 :)

(: Operators: +, -, *, div, mod :)
10 + 5   (: 15 :)
10 - 5   (: 5 :)
10 * 5   (: 50 :)
10 div 5 (: 2 :)
10 mod 3 (: 1 :)