XQuery Functions

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XQuery Basic
XQuery HOME
XQuery Intro
XQuery Example
XQuery FLWOR
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XQuery Functions
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# XQuery Functions

XQuery 1.0, XPath 2.0, and XSLT 2.0 share the same functions library.

## XQuery Functions

XQuery includes over 100 built-in functions. There are functions for string values, numeric values, date and time comparison, node and QName manipulation, sequence manipulation, Boolean values, and more. You can also define your own functions in XQuery.

## XQuery Built-in Functions

The URI of the XQuery function namespace is:
http://www.w3.org/2005/02/xpath-functions

The default prefix for the function namespace is fn:.

Tip: Functions are often called with the fn: prefix, such as fn:string(). However, since fn: is the default prefix of the namespace, the function names do not need to be prefixed when called.

The reference of all the built-in XQuery 1.0 functions is located in our XPath tutorial.

## Examples of Function Calls

A call to a function can appear where an expression may appear. Look at the examples below:

Example 1: In an element

    <name>{uppercase($booktitle)}</name>

Example 2: In the predicate of a path expression

    doc("books.xml")/bookstore/book[substring(title,1,5)='Harry']

Example 3: In a let clause

    let $name := (substring($booktitle,1,4))

## XQuery User-Defined Functions

If you cannot find the XQuery function you need, you can write your own.

User-defined functions can be defined in the query or in a separate library.

### Syntax

    declare function prefix:function_name($parameter AS datatype)
      AS returnDatatype
    {

    (: ...function code here... :)

    };

Notes on user-defined functions:

- Use the declare function keyword
- The name of the function must be prefixed
- The data type of the parameters are mostly the same as the data types defined in XML Schema
- The body of the function must be surrounded by curly braces

### Example of a User-defined Function Declared in the Query

    declare function local:minPrice(
      $price as xs:decimal?,
      $discount as xs:decimal?)
      AS xs:decimal?
    {
    let $disc := ($price * $discount) div 100
    return ($price - $disc)
    };

    (: Below is an example of how to call the function above :)

    <minPrice>{local:minPrice($book/price, $book/discount)}</minPrice>

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