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This article is part of the [[XQuery|XQuery Portal]]. It summarizes provides a summary of the most interesting important features of the [httphttps://www.w3.org/TR/xquery-30/ XQuery 3.0] RecommendationsRecommendation.
=Enhanced FLWOR Expressions=
'''Example:'''
<pre classsyntaxhighlight lang="brush:xquery">
for $country in db:open('factbook')//country
where $country/@population > 100000000
count $id
return <country id='{ $id }' name='{ $name }'>{ $city/name }</country>
</presyntaxhighlight>
==group by==
FLWOR expressions have been extended to include the [httphttps://www.w3.org/TR/xquery-30/#id-group-by group by] clause, which is well-established in SQL. <code>group by</code> can be used to apply value-based partitioning to query results:
'''XQuery:'''
<pre classsyntaxhighlight lang="brush:xquery">
for $ppl in doc('xmark')//people/person
let $ic := $ppl/profile/@income
order by $income
return element { $income } { count($ppl) }
</presyntaxhighlight>
This query is a rewrite of [httphttps://www.ins.cwi.nl/projects/xmark/Assets/xmlquery.txt Query #20] contained in the [httphttps://www.insprojects.cwi.nl/projectsxmark/xmark XMark Benchmark Suite] to use <code>group by</code>.
The query partitions the customers based on their income.
'''Result:'''
<pre classsyntaxhighlight lang="brush:xml">
<challenge>4731</challenge>
<na>12677</na>
<preferred>314</preferred>
<standard>7778</standard>
</presyntaxhighlight>
In contrast to the relational GROUP BY statement, the XQuery counterpart concatenates the values of all non-grouping variables that belong to a specific group. In the context of our example, all nodes in <code>//people/person</code> that belong to the <code>preferred</code> partition are concatenated in <code class="brush:xquery">$ppl</code> after grouping has finished. You can see this effect by changing the return statement to:
<pre classsyntaxhighlight lang="brush:xquery">
...
return element { $income } { $ppl }
</presyntaxhighlight>
'''Result:'''
<pre classsyntaxhighlight lang="brush:xml">
<challenge>
<person id="person0">
…
</challenge>
</presyntaxhighlight>
Moreover, a value can be assigned to the grouping variable. This is shown in the following example:
'''XQuery:'''
<pre classsyntaxhighlight lang="brush:xquery">
let $data :=
<xml>
$person/@name ! element name { data() }
}
</presyntaxhighlight>
'''Result:'''
<pre classsyntaxhighlight lang="brush:xml">
<persons country="USA">
<name>John</name>
<name>Johann</name>
</persons>
</presyntaxhighlight>
==count==
The {{Code|count}} clause enhances the FLWOR expression with a variable that enumerates the iterated tuples.
<pre classsyntaxhighlight lang="brush:xquery">
for $n in (1 to 10)[. mod 2 = 1]
count $c
return <<number count="{ $c }" number="{ $n }"/>></presyntaxhighlight>
==allowing empty==
The {{Code|allowing empty}} provides functionality similar to outer joins in SQL:
<pre classsyntaxhighlight lang="brush:xquery">
for $n allowing empty in ()
return 'empty? ' || empty($n)
</presyntaxhighlight>
==window==
Window clauses provide a rich set of variable declarations to process sub-sequences of iterated tuples. An example:
<pre classsyntaxhighlight lang="brush:xquery">
for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
start at $s when fn:true()
only end at $e when $e - $s eq 2
return <<window>>{ $w }<</window>></presyntaxhighlight>
More information on window clauses, and all other enhancements, can be found in the [httphttps://www.w3.org/TR/xquery-30/#id-windows specification].
=Function Items=
<ul>
<li>Declaring a new ''inline function'':
<pre classsyntaxhighlight lang="brush:xquery">let $f := function($x, $y) { $x + $y }return $f(17, 25)</presyntaxhighlight>
'''Result:''' <code>42</code>
</li>
<li>Getting the function item of an existing (built-in or user-defined) XQuery function. The arity (number of arguments) has to be specified as there can be more than one function with the same name:
<pre classsyntaxhighlight lang="brush:xquery">let $f := math:pow#2return $f(5, 2)</presyntaxhighlight>
'''Result:''' <code>25</code>
</li>
<li>''Partially applying'' another function or function item. This is done by supplying only some of the required arguments, writing the placeholder <code>?</code> in the positions of the arguments left out. The produced function item has one argument for every placeholder.
<pre classsyntaxhighlight lang="brush:xquery">let $f := fn:substring(?, 1, 3)
return (
$f('foo123'),
$f('bar456')
)</presyntaxhighlight>
'''Result:''' <code>foo bar</code>
</li>
=Simple Map Operator=
The [httphttps://www.w3.org/TR/xquery-30/#id-map-operator simple map] operator {{Code|!}} provides a compact notation for applying the results of a first to a second expression: the resulting items of the first expression are bound to the context item one by one, and the second expression is evaluated for each item. The map operator may be used as replacement for FLWOR expressions:
'''Example:'''
<pre classsyntaxhighlight lang="brush:xquery">
(: Simple map notation :)
(1 to 10) ! element node { . },
for $i in 1 to 10
return element node { $i }
</presyntaxhighlight>
In contrast to path expressions, the results of the map operator will not be made duplicate-free and returned in document order.
=Try/Catch=
The [httphttps://www.w3.org/TR/xquery-30/#id-try-catch try/catch] construct can be used to handle errors at runtime:
'''Example:'''
<pre classsyntaxhighlight lang="brush:xquery">
try {
1 + '2'
'Error [' || $err:code || ']: ' || $err:description
}
</presyntaxhighlight>
'''Result:''' <code>Typing error: '+' operator: number expected, xs:string found.</code>
=Switch=
The [httphttps://www.w3.org/TR/xquery-30/#id-switch switch] statement is available in many other programming languages. It chooses one of several expressions to evaluate based on its input value.
'''Example:'''
<pre classsyntaxhighlight lang="brush:xquery">
for $fruit in ("Apple", "Pear", "Peach")
return switch ($fruit)
case "Peach" return "pink"
default return "unknown"
</presyntaxhighlight>
'''Result:''' <code>red green pink</code>
'''Example:'''
<pre classsyntaxhighlight lang="brush:xquery">
for $fruit in ("Apple", "Cherry")
return switch ($fruit)
default
return "unknown"
</presyntaxhighlight>
'''Result:''' <code>red red</code>
New namespaces can be created via so-called 'Computed Namespace Constructors'.
<pre classsyntaxhighlight lang="brush:xquery">
element node { namespace pref { 'http://url.org/' } }
</presyntaxhighlight>
=String Concatenations=
Two vertical bars <code>||</code> (also named ''pipe characters'') can be used to concatenate strings. This operator is a shortcut for the {{Code|fn:concat()}} function.
<pre classsyntaxhighlight lang="brush:xquery">
'Hello' || ' ' || 'Universe'
</presyntaxhighlight>
=External Variables=
Default values can be attached to external variable declarations. This way, an expression can also be evaluated if its external variables have not been bound to a new value.
<pre classsyntaxhighlight lang="brush:xquery">
declare variable $user external := "admin";
"User:", $user
</presyntaxhighlight>
=Serialization=
'''Example:'''
<pre classsyntaxhighlight lang="brush:xquery">
declare namespace output = "http://www.w3.org/2010/xslt-xquery-serialization";
declare option output:omit-xml-declaration "no";
declare option output:method "xhtml";
'''Result:''' <code><?xml version="1.0" encoding="UTF-8"?><html></html></code>
'''Example:'''
<pre classsyntaxhighlight lang="brush:xquery">
declare context item := document {
<xml>
for $t in .//text()
return string-length($t)
</presyntaxhighlight>
'''Result:''' <code>5 5</code>
'''Example:'''
<pre classsyntaxhighlight lang="brush:xquery">
declare %private function local:max($x1, $x2) {
if($x1 > $x2) then $x1 else $x2
local:max(2, 3)
</presyntaxhighlight>
=Functions=
The following functions have been added in the [httphttps://www.w3.org/TR/xpath-functions-3031/ XQuery 3.0 Functions and Operators] Specification:
<code>fn:analyze-string</code>* <code>fn:available-environment-variables</code>, <code>fn:element-with-id</code>, <code>fn:environment-variable</code>, <code>fn:filter</code>, <code>fn:fold-left</code>, <code>fn:fold-right</code>, <code>fn:for-each</code>, <code>fn:for-each-pair</code>, <code>fn:format-date</code>, <code>fn:format-dateTime</code>, <code>fn:format-integer</code>, <code>fn:format-number</code>, <code>fn:format-time</code>, <code>fn:function-arity</code>, <code>fn:function-lookup</code>, <code>fn:function-name</code>, <code>fn:generate-id</code>, <code>fn:has-children</code>, <code>fn:head</code>, <code>fn:innermost</code>, <code>fn:outermost</code>, <code>fn:parse-xml</code>, <code>fn:parse-xml-fragment</code>, <code>fn:path</code>, <code>fn:serialize</code>, <code>fn:tail</code>, <code>fn:unparsed-text</code>, <code>fn:unparsed-text-available</code>, <code>fn:unparsed-text-lines</code>, <code>fn:uri-collection</code>
