XQuery Functions

⚡ What are XQuery Functions?

XQuery functions are reusable code blocks that perform specific operations on data. They include built-in functions for strings, numbers, dates, and sequences, plus the ability to create custom functions for specialized tasks.


(: Using a built-in function :)
count(//book)
concat("Hello", " ", "World")

Function Categories

XQuery provides a rich library of built-in functions organized by data type and purpose. These functions simplify common operations and data transformations.

🔤

String Functions

Manipulate text data

concat(), substring()

🔢

Numeric Functions

Perform calculations

sum(), avg(), round()

📋

Sequence Functions

Work with collections

count(), distinct-values()

🔧

Custom Functions

Create your own functions

declare function

🔹 String Functions

Common functions for text manipulation:

(: Concatenate strings :)
concat("Hello", " ", "World")
(: Result: "Hello World" :)

(: Get string length :)
string-length("XQuery")
(: Result: 6 :)

(: Extract substring :)
substring("XQuery", 1, 3)
(: Result: "XQu" :)

(: Convert to uppercase :)
upper-case("hello")
(: Result: "HELLO" :)

(: Convert to lowercase :)
lower-case("HELLO")
(: Result: "hello" :)

(: Check if contains :)
contains("XQuery", "Query")
(: Result: true :)

🔹 Numeric Functions

Functions for mathematical operations:

(: Sum of values :)
sum(//book/price)
(: Result: 149.95 :)

(: Average value :)
avg(//book/price)
(: Result: 29.99 :)

(: Maximum value :)
max(//book/price)
(: Result: 39.99 :)

(: Minimum value :)
min(//book/price)
(: Result: 19.99 :)

(: Round number :)
round(29.567)
(: Result: 30 :)

(: Ceiling and floor :)
ceiling(29.1)  (: 30 :)
floor(29.9)    (: 29 :)

Example:

let $prices := (19.99, 29.99, 39.99)
return
  <summary>
    <total>{sum($prices)}</total>
    <average>{avg($prices)}</average>
  </summary>

🔹 Sequence Functions

Functions for working with sequences:

(: Count items :)
count(//book)
(: Result: 5 :)

(: Get distinct values :)
distinct-values(//book/author)
(: Result: unique authors :)

(: Check if empty :)
empty(//book[@id="999"])
(: Result: true :)

(: Check if exists :)
exists(//book[@id="1"])
(: Result: true :)

(: Reverse sequence :)
reverse((1, 2, 3, 4, 5))
(: Result: (5, 4, 3, 2, 1) :)

(: Remove duplicates :)
distinct-values((1, 2, 2, 3, 3, 3))
(: Result: (1, 2, 3) :)

🔹 Boolean Functions

Functions that return true or false:

(: Check if true :)
boolean(//book[@price < 30])
(: Result: true if any book under $30 :)

(: Not function :)
not(empty(//book))
(: Result: true if books exist :)

(: Starts with :)
starts-with("XQuery", "XQ")
(: Result: true :)

(: Ends with :)
ends-with("XQuery", "ery")
(: Result: true :)

🔹 Node Functions

Functions for working with XML nodes:

(: Get node name :)
name(//book[1])
(: Result: "book" :)

(: Get local name :)
local-name(//book[1])
(: Result: "book" :)

(: Get text content :)
data(//book/title)
(: Result: title text values :)

(: Get string value :)
string(//book[1]/title)
(: Result: first book title as string :)

🔹 Custom Functions

Create your own reusable functions:

(: Declare a custom function :)
declare function local:discount($price) {
  $price * 0.9
};

(: Use the function :)
for $book in //book
return
  <book>
    <title>{$book/title}</title>
    <original>{$book/price}</original>
    <discounted>{local:discount($book/price)}</discounted>
  </book>

(: Function with multiple parameters :)
declare function local:fullName($first, $last) {
  concat($first, " ", $last)
};

local:fullName("John", "Doe")
(: Result: "John Doe" :)

🔹 Aggregate Functions

Functions for data aggregation:

(: Total price of all books :)
<total>{sum(//book/price)}</total>

(: Average price by category :)
for $cat in distinct-values(//book/@category)
return
  <category name="{$cat}">
    <avgPrice>{avg(//book[@category=$cat]/price)}</avgPrice>
    <count>{count(//book[@category=$cat])}</count>
  </category>