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.
You can also define your own functions in XQuery.
XQuery Data Types
XQuery shares the same data types as XML Schema 1.0 (XSD).
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>
