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A new The {{Code|count}} clause enhances the FLWOR expression with a variable that enumerates the iterated tuples.
A map operator is defined to be part of a path expression, which may now mix path and map operators. In contrast to the path operatorexpressions, the results of the map operator will not be made duplicate-free and returned in document order.
The syntax differed in older versions of the XQuery 3.0 specification, in which the prefixed namespace URI was quoted:
* <code><nowiki>"http://www.w3.org/2005/xpath-functions/math":pi()</nowiki></code>
* <code>"java:java.io.FileOutputStream":new("output")</code>
<<html/>></presyntaxhighlight>
→window
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] Recommendations.XQuery 3.0 is fully supported by BaseXRecommendation.
=Enhanced FLWOR Expressions=
Most clauses of FLWOR expressions can now be specified in an arbitrary order: additional {{Code|let}} and {{Code|for}} clauses can be put after a {{Code|where}} clause, and multiple {{Code|where}}, {{Code|order by}} and {{Code|group by}} statements can be used. This means that many nested loops can now be rewritten to a single FLWOR expression.
'''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 counterpartconcatenates 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==
<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>
=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>
=Expanded QNames=
A ''QName'' can now be directly prefixed with the letter "Q" and a namespace URI in the [http://www.jclark.com/xml/xmlns.htm Clark Notation].
'''Examples:'''
* <code><nowiki>Q{http://www.w3.org/2005/xpath-functions/math}pi()</nowiki></code> returns the number π
* <code>Q{java:java.io.FileOutputStream}new("output.txt")</code> creates a new Java file output stream
=Namespace Constructors=
New namespaces can now 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 now 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=
[[Serialization|Serialization ]]parameters can now be defined in within XQuery expressions. Parameters are placed in the query prolog and need to be specified as option declarations, using the <code>output</code> prefix.
'''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>
=Context Item=
The context item can now be specified in the prolog of an XQuery expression:
'''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 $x2
local:max(2, 3)
</presyntaxhighlight> The following implementation-defined annotations are available: * {{Code|%basex:inline([limit])}} enforces the inlining of a function. Example: '''Example:''' <pre class="brush:xquery">declare option db:inlinelimit '0';declare %basex:inline function local:id($x) { $x };local:id(123)</pre> In this query, function inlining has been deactivated by setting [[Options#INLINELIMIT|inlinelimit]] to {{Code|0}}. The annotation enforces inlining for the given function, though, resulting in the optimized query expression {{Code|123}}. If an integer is specified as annotation argument, it will be interpreted a local inline limit. * {{Code|%basex:lazy}} enforces the lazy evaluation of a global variable. Example: '''Example:''' <pre class="brush:xquery">declare %basex:lazy variable $january := doc('does-not-exist');if(month-from-date(current-date()) == 1) then $january else ()</pre> The annotation ensures that an error will only be thrown if the condition yields true. Without the annotation, the error will always be thrown, because the referenced document is not found.
=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:formatfor-dateeach</code>, <code>fn:formatfor-each-dateTimepair</code>, <code>fn:format-integerdate</code>, <code>fn:format-numberdateTime</code>, <code>fn:format-timeinteger</code>, <code>fn:functionformat-aritynumber</code>, <code>fn:functionformat-lookuptime</code>, <code>fn:function-namearity</code>, <code>fn:generatefunction-idlookup</code>, <code>fn:hasfunction-childrenname</code>, <code>fn:headgenerate-id</code>, <code>fn:innermosthas-children</code>, <code>fn:maphead</code>, <code>fn:map-pairsinnermost</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>
New signatures have been added for the following functions:
=Changelog=
;Version 8.4
* Added: %non-deterministic
;Version 8.0
