XQuery 3.0
This article is part of the Query Portal. It summarizes features of the upcoming W3C XQuery 3.0 Recommendation 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 (see Serialization for more details). 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 all new functions of the XQuery 3.0 Functions and Operators draft that are already supported in BaseX.
The following functions have been added:
math:pi()
,math:sin()
, and many others (see Math Functions)fn:head()
fn:tail()
fn:generate-id()
fn:analyze-string()
fn:environment-variable()
fn:available-environment-variables()
fn:unparsed-text-available()
fn:unparsed-text-lines()
fn:unparsed-text()
fn:element-with-id()
fn:parse-xml()
fn:uri-collection()
fn:serialize()
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
The following functions are partially supported:
fn:format-integer()
fn:format-number()
fn:format-dateTime()
fn:format-date()
fn:format-time()