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XQuery 1.0, XPath 2.0, and XSLT 2.0 share the same functions library
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 shares the same data types as XML Schema 1.0 (XSD).
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))
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($parameter as datatype)
as returnDatatype
{
...function code here...
};
Notes on user-defined functions:
Example of a User-defined Function Declared in the Query
declare function local:minPrice($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>