XQuery 3.0
This article is part of the Query Portal. It summarizes features of the upcoming XQuery 3.0 and XPath 2.0 Recommendations that have already been implemented in BaseX.
Group By
FLWOR expressions have been extended to include the group by clause, which is well-established among relational database systems. group by can be used to apply value-based partitioning to query results:
Example:
for $ppl in doc('xmark')//people/person
let $ic := $ppl/profile/@income
let $income := if($ic < 30000) then
"challenge"
else if($ic >= 30000 and $ic < 100000) then
"standard"
else if($ic >= 100000) then
"preferred"
else
"na"
group by $income
order by $income
return element { $income } { count($ppl) }
This query is a rewrite of Query #20 contained in the XMark Benchmark Suite to use group by.
The query partitions the customers based on their income.
Result:
<challenge>4731</challenge> <na>12677</na> <prefered>314</prefered> <standard>7778</standard>
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 //people/person that belong to the "preferred" partition are concatenated in $ppl after grouping has finished.
You can see this effect by changing the return statement to:
...
return element { $income } { $ppl }
Result:
<challenge>
<person id="person0">
<name>Kasidit Treweek</name>
…
<person id="personX">
…
</challenge>
Try/Catch
The try/catch construct can be used to handle errors at runtime:
Example:
try {
1 + '2'
} catch *($code, $desc) {
concat('Error [', $code, ']: ', $desc)
}
Result: Error [XPTY0004]: '+' operator: number expected, string found.
Switch
The switch statement is available in many other programming languages. It chooses one of several expressions to evaluate based on its input value.
Example:
for $fruit in ("Apple", "Pear", "Peach")
return switch ($fruit)
case "Apple" return "red"
case "Pear" return "green"
case "Peach" return "pink"
default return "unknown"
Result: red green pink
Serialization
Serialization parameters can now be defined within XQuery expressions. Parameters are placed in the query prolog and need to be specified as option declarations, using the output prefix.
Example:
declare option output:omit-xml-declaration "no"; declare option output:method "xhtml"; <html/>
Result: <?xml version="1.0" encoding="UTF-8"?><html></html>
Functions
This paragraph lists functions that have been added in Version 3.0 of the XQuery Functions and Operators Working Draft.
The following functions have been added:
math:pi(),math:sin(), and many others (see Math Functions)fn:analyze-string()fn:available-environment-variables()fn:element-with-id()fn:environment-variable()fn:filter()fn:fold-left()fn:fold-right()fn:format-date()fn:format-dateTime()fn:format-integer()fn:format-number()fn:format-time()fn:function-arity()fn:function-name()fn:generate-id()fn:has-children()fn:head()fn:innermost()fn:map()fn:map-pairs()fn:outermost()fn:parse-xml()fn:path()fn:serialize()fn:tail()fn:unparsed-text()fn:unparsed-text-available()fn:unparsed-text-lines()fn:uri-collection()
New signatures have been added for the following functions:
fn:document-uri()with 0 argumentsfn:string-join()with 1 argumentfn:node-name()with 0 argumentsfn:round()with 2 argumentsfn:data()with 0 arguments
