eXist Xquery Examples

以下ex:>代表输入表达式 re:>表示输出结果

--插入[使用exist的xquery数据库检索工具]说明--

[基础操作]

1 条件表达式

ex:>if(3 < 4) then 'yes!' else 'no!'

re:>yes!

ex:>

for$x in (-1.5, 0.4, 1.7)

return<amount>

{

if($x < 0)

thenconcat('(', -$x, ')')

else$x

}</amount>

re:>

说明：注意第一行的输出和其它两行有所不同

-$x对$x取反

2 定义本地变量

ex:>let$x := 5 let $y := 6 return 10*$x+$y

re:>56

3 使用','，其功能相当于数组

ex:>3,4,5

re:>3

扩展加入其它语句

ex:>3,4,5,let$t:=56 return $t

re:>3

4 在return中使用{} {expression} 执行出来表达式的结果

ex:>

let$i := 2 return

let$r := Value

return

{$r} of 10*{$i} is{10*$i}.

re:>

Value of 10*2is 20.

5 简单循环语句

ex:>for$x in (1 to 3) return ($x,10+$x)

re:>1

ex:>for$speech in document('/db/tonybooks/Catalog.xml')//categoryName

return {$speech}

re:>略

ex:>

<html>{

let$book := document('mybook.xml')/book

for$ch in $book/chapter

return <h2>{$ch/title)</h2>

}</html>

re:>略

6 使用text(),返回内容

ex:>let$book:=document('examples.xml')/example-queries/query

return$book/code/text()

ex:>let$doc := document('examples.xml')//query/code/text()

return$doc

[函数的定义与调用] ex:>

declarenamespace jnb = 'http://ociweb.com/jnb';

declarevariable $jnb:pi as xs:decimal { 3.1416 };

declarefunction jnb:fib($i as xs:integer) as xs:integer {

if ($i = 0 or $i = 1)

then1

else jnb:fib($i - 1) + jnb:fib($i - 2)

};

jnb:fib(3),jnb:fib(4), jnb:fib(5), $jnb:pi

re:>

3.1416

[节点和节点类型 ]一下两个作用相同

ex:><greetingfrom='weiqi'>Hello, World!</greeting>

re:><greetingfrom='weiqi'>Hello, World!</greeting>

ex:>document {

element { 'greeting' } {

attribute { 'from ' } {'weiqi' },

'Hello, World!'

}

re:><greetingfrom ='weiqi'>Hello, World!</greeting>

[flwor表达式/数据库检索命令]标准类型for, let,where, order by, return

1for语句

ex:>

for$x in (1, 2, 3)

return<number>{ $x }</number>

re:>

2let语句

ex:>

let$a := (1, 2, 3)

return<numbers>{ $a }</numbers>

re:><numbers>12 3</numbers>

3where语句

ex:>

for$x in (1, 2, 3)

where$x >= 2

return <number>{ $x}</number>

re:>

4order by 语句

ex:>

for$x in (<greeting/>, <greeting from='weiqi'/>,<greeting from='brian'/>)

orderby $x/@from ascending empty least

return$x

re:>

<greetingfrom='brian'/>

<greetingfrom='weiqi'/>

说明order by 有以下几个属性：

descending，ascending，empty greatest，empty least

分别测试一下

[数量操作]该操作非常有用该操作非常有用1some 和 every 例子

ex:>some$x in (1, 2, 3) satisfies $x >= 2

re:>true

ex:>every$x in (1, 2, 3) satisfies $x >= 2

re:>false

ex:>some$x in (1, 2, 3), $y in (3, 4, 5) satisfies $x = $y

re:>true

ex:>every$x in (1, 2, 3), $y in (3, 4, 5) satisfies $x = $y

re:>false

2count($a)

ex:>let$a:=collection('tonybooks')//category

returncount($a)

re:>返回40个1

ex:>for$a in collection('tonybooks')//category

returncount($a)

re:>返回40

区别以上例子

3 多重循环语句

ex:>

for$c in customers

for$o in orders

where$c.cust_id=$o.cust_id and $o.part_id='xx'

return$c.name

以上语句等价于sql语句

selectcustomers.name from customers, orders

wherecustomers.cust_id=orders.cust_id andorders.part_id='xx'

ex:>

for$book in bib.xml//book

let$title := $book/title

where$book/publisher = 'Addison-Wesley'

return

<bookInfo>{$title }</bookInfo>

[xpath例子] greetings.xml:

<?xmlversion='1.0' encoding='UTF-8'?>

<greetingfrom='weiqi'>Nihao!</greeting>

<greetingfrom='brian'>Hi!</greeting>

<greetingfrom='luc'>Bonjour!</greeting>

</greetings>

ex:>doc('greetings.xml')/greetings

re:><greetings>

<greetingfrom='weiqi'>Nihao!</greeting>

<greetingfrom='brian'>Hi!</greeting>

<greetingfrom='luc'>Bonjour!</greeting>

</greetings>

ex:>doc('greetings.xml')//greeting

re:><greetingfrom='weiqi'>Nihao!</greeting>

<greetingfrom='luc'>Bonjour!</greeting>

说明：注意以上两个例子的区别/greetings和//greetings，

前者表示从根节点开始逐级遍历，后者表示任何级的节点都遍历

ex:>doc('greetings.xml')//greeting[@from='weiqi']

re:><greetingfrom='weiqi'>Nihao!</greeting>

说明：@from 用来引用节点中的属性名称

引用节点名直接输入例如：greeting 或者 greetings就可以

ex:>doc('greetings.xml')//greeting/@from

re:>from='weiqi'from='brian' from='luc'

ex:>doc('greetings.xml')//greeting[1]

re:><greetingfrom='weiqi>Nihao!</greeting>

说明：使用'节点名'[n]表示输出第几个节点内容

待查：

let$a := 3,4 --错误

let$b := ($a, $a)

let$c := 99

let$d := ()

return(count($a), count($b), count($c), count($d))

evaluatesto (2, 4, 1, 0) because $b is the same as (3,4,3,4).

待查：

children(Thisis very cool.)

returnsthis sequence of 3 values:

'Thisis ', very, ' cool.'

================以下为未整理部分=============

[Modules]

You can put functions and variablesdeclarations into library modules. A library module is a file that starts witha module namespace declaration and contains declarations of functions,variables, etc., but does not contain an expression at the end. A main modulecontains an expression at the end. Both library modules and main modules canimport other library modules to access variables and functions declared in theimported module.

(: libfib.xq :)

module namespace jnb ='http://ociweb.com/jnb';

declare function jnb:fib($i as xs:integer)as xs:integer {

if($i <= 1)

then 1

else jnb:fib($i - 1) + jnb:fib($i - 2)

};

(: mainfib.xq: )

import module namespace jnb ='http://ociweb.com/jnb' at 'libfib.xq';

jnb:fib(6)

[weiqi@gao] $ xquery mainfib.xq # Saxon

Qexo supports compiled modules. A librarymodule is compiled to a Java class whose name is derived from the modulenamespace URI. A main module is compiled to a Java class whose name is derivedfrom the module file name.

[weiqi@gao] $ qexo -C libfib.xq # Compile to Java classcom.ociweb.jnb

(compiling libfib.xq)

[weiqi@gao] $ qexo --main -Cmainfib.xq # Compile to Java classmainfib

(compiling mainfib.xq)

[weiqi@gao] $ java mainfib

-------------------------------------------------------------------------

Type Specification

XQuery is a strongly typed programminglanguage. Like Java and C#, for example, it's a mix of static typing (typeconsistency checked at compile-time) and dynamic typing (run-time type tests).However, the types in XQuery are different from the classes familiar fromobject-oriented programming. Instead, it has types to match XQuery's datamodel, and it allows you to import types form XML Schema.

if ($child instance of element section)

then process-section($child)

else ( ) {--nothing--}

This invokes the process-section functionif the value of $child is an element whose tag name is section. XQuery has aconvenient typeswitch shorthand for matching a value against a number of types.The following converts a set of tag names to a different set.

define function convert($x) {

typeswitch ($x)

case element para return {process-children($x)}

case element emph return{process-children($x)}

default return process-children($x)

}

define function process-children($x) {

for$ch in children($x)

return convert($ch)

}

Hello,

I am a beginner in Xquery.

In my schema I have element which has IDREFattribute.I want to extract id value to which points and check whether thatvalue is equivalent to some value.

eg:

<FNAME>smith</FNAME>

</AUTHOR>

<MAINATHR>SHARMA</MAINATHR>

</PAPER>

<MAINATHR>SHARMA</MAINATHR>

</PAPER>

let $id := 'sai@yahoo.com',

for $paper in $doc/PAPER[@EMAILID = $id],

for $author in $doc/AUTHOR[@EMAILID = $id]

return

<resultPAPERID='{$paper/@PAPERID}'>

{$author/FNAME}

for $paper in $doc/PAPER,

for $author in $doc/AUTHOR

where $paper/@EMAILID = $auther/$EMAILID

return

{$author/FNAME}

如上例程序，在xquery中引用节点和节点属性名称的时候稍有不同。

节点 paper 属性 @paper

I am completely new to XQuery..

I have the following which I would like torun on an .xml file...

for $book in bib.xml//book

let $title := $book/title

where $book/publisher = 'Addison-Wesley'

return

{ $title }

</bookInfo>

and the bib.xml file

<bib>

<title>TCP/IPIllustrated</title>

<author><last>Stevens</last><first>W.</first></author>

<publisher>Addison-Wesley</publisher>

</book>

<title>Advanced Programming in theUnix environment</title>

<author><last>Stevens</last><first>W.</first></author>

<publisher>Addison-Wesley</publisher>

</book>

<author><last>Abiteboul</last><first>Serge</first></author>

<author><last>Buneman</last><first>Peter</first></author>

<author><last>Suciu</last><first>Dan</first></author>

<publisher>Morgan KaufmannPublishers</publisher>

</book>

<title>The Economics of Technologyand Content for Digital TV</title>

<last>Gerbarg</last><first>Darcy</first>

</editor>

<publisher>Kluwer AcademicPublishers</publisher>

</book>

</bib>

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最后附上一个好的教材：

http://monetdb.cwi.nl/XQuery/Demo/index.html

http://www.xml.com/pub/a/2005/03/02/xquery.html

http://www.xml.com/pub/a/2005/03/23/xquery-2.html

http://www.w3schools.com/xquery/default.asp