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<h1>XQuery Functions</h1>
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<p class="intro">XQuery 1.0, XPath 2.0, and XSLT 2.0 share the same functions library.</p>
<hr />
<h2>XQuery Functions</h2>
<p>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.</p>
<hr />
<h2>XQuery Built-in Functions</h2>
<p>The URI of the XQuery function namespace is:<br />
http://www.w3.org/2005/02/xpath-functions</p>
<p>The default prefix for the function namespace is fn:.</p>
<p><b>Tip:</b> 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.</p>
<p><a href="../xpath/xpath_functions.asp">The reference of all the built-in XQuery 1.0 functions is located
in our XPath tutorial</a>.</p>
<hr />
<h2>Examples of Function Calls</h2>
<p>A call to a function can appear where an expression may appear. Look at the
examples below:</p>
<p>Example 1: In an element</p>
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<pre><name>{uppercase($booktitle)}</name></pre>
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<p>Example 2: In the predicate of a path expression</p>
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<pre>doc("books.xml")/bookstore/book[substring(title,1,5)='Harry']</pre>
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<p>Example 3: In a let clause</p>
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<pre>let $name := (substring($booktitle,1,4))</pre>
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<h2>XQuery User-Defined Functions</h2>
<p>If you cannot find the XQuery function you need, you can write
your own.</p>
<p>User-defined functions can be defined in the query or in a separate library.</p>
<h3>Syntax</h3>
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<pre>declare function <i>prefix:function_name</i>($<i>parameter </i>AS<i> datatype</i>)
AS <i>returnDatatype</i>
{</pre>
<pre>(: ...function code here... :)</pre>
<pre>};</pre>
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<p>Notes on user-defined functions: </p>
<ul>
<li>Use the declare function keyword</li>
<li>The name of the function must be prefixed</li>
<li>The data type of the parameters are mostly the same as the data types
defined in XML Schema</li>
<li>The body of the function must be surrounded by curly braces</li>
</ul>
<h3>Example of a User-defined Function Declared in the Query</h3>
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<pre>declare function local:minPrice(
$price as xs:decimal?,
$discount as xs:decimal?)
AS xs:decimal?
{
let $disc := ($price * $discount) div 100
return ($price - $disc)
};</pre>
<pre>(: Below is an example of how to call the function above :)</pre>
<pre><minPrice>{local:minPrice($book/price, $book/discount)}</minPrice></pre>
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