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XQuery Functions


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


XQuery函数

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运算子

XPath Functions

You can also define your own functions in XQuery.


XQuery Data Types

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

XSD字串

XSD日期

XSD数值

XSD杂项


示例 of 函数调用s

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...
};

笔记 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模式
  • 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>




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