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XQuery Functions


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


XQuery Functions

XQuery is built on XPath expressions. XQuery 1.0 and XPath 2.0 share the same data model and support the same functions and operators.

XPath Operators

XPath Functions

You can also define your own functions in XQuery.


XQuery Data Types

XQuery shares the same data types as XML Schema 1.0 (XSD).

XSD String

XSD Date

XSD Numeric

XSD Misc


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>{upper-case($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($p as xs:decimal?,$d as xs:decimal?)
as xs:decimal?
{
let $disc := ($p * $d) div 100
return ($p - $disc)
};

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

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