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

{

($x < 0)

then

concat("(", -$x, ")")

else

}

</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*2

is 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:>

declare

namespace jnb = "http://ociweb.com/jnb";

declare

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

declare

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

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

then

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:><greeting

from="weiqi">Hello, World!</greeting>

re:><greeting

from="weiqi">Hello, World!</greeting>

ex:>

document {

element { "greeting" } {

attribute { "from " } {

"weiqi" },

"Hello, World!"

}

re:><greeting

from ="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

for语句

ex:>

for

$x in (1, 2, 3)

return

re:>

let语句

ex:>

let

$a := (1, 2, 3)

return

re:><numbers>1

2 3</numbers>

where语句

ex:>

for

$x in (1, 2, 3)

where

$x >= 2

return <number>{ $x

}</number>

re:>

order by 语句

ex:>

for

$x in (<greeting/>, <greeting from="weiqi"/>,

<greeting from="brian"/>)

order

by $x/@from ascending empty least

return

re:>

<greeting

from="brian"/>

<greeting

from="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

some 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

count($a)

ex:>let

$a:=collection("tonybooks")//category

return

count($a)

re:>返回40个1

ex:>for

$a in collection("tonybooks")//category

return

count($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

select

customers.name from customers, orders

where

customers.cust_id=orders.cust_id and

orders.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:

<?xml

version="1.0" encoding="UTF-8"?>

<greeting

from="weiqi">Nihao!</greeting>

<greeting

from="brian">Hi!</greeting>

<greeting

from="luc">Bonjour!</greeting>

</greetings>

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

re:><greetings>

<greeting

from="weiqi">Nihao!</greeting>

<greeting

from="brian">Hi!</greeting>

<greeting

from="luc">Bonjour!</greeting>

</greetings>

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

re:><greeting

from="weiqi">Nihao!</greeting>

<greeting

from="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:><greeting

from="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:><greeting

from="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))

evaluates

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

待查：

children(This

is very cool.)

returns

this sequence of 3 values:

"This

is ", very, " cool."

================以下为未整理部分=============

[Modules]

You can put functions and variables

declarations into library modules. A library module is a file that starts with

a module namespace declaration and contains declarations of functions,

variables, etc., but does not contain an expression at the end. A main module

contains an expression at the end. Both library modules and main modules can

import other library modules to access variables and functions declared in the

imported module.

(: libfib.xq :)

module namespace jnb =

"http://ociweb.com/jnb";

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

as xs:integer {

($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 library

module is compiled to a Java class whose name is derived from the module

namespace URI. A main module is compiled to a Java class whose name is derived

from the module file name.

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

com.ociweb.jnb

(compiling libfib.xq)

[weiqi@gao] $ qexo --main -C

mainfib.xq # Compile to Java class

mainfib

(compiling mainfib.xq)

[weiqi@gao] $ java mainfib

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

Type Specification

XQuery is a strongly typed programming

language. Like Java and C#, for example, it's a mix of static typing (type

consistency checked at compile-time) and dynamic typing (run-time type tests).

However, the types in XQuery are different from the classes familiar from

object-oriented programming. Instead, it has types to match XQuery's data

model, 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 function

if the value of $child is an element whose tag name is section. XQuery has a

convenient 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 IDREF

attribute.I want to extract id value to which points and check whether that

value is equivalent to some value.

eg:

<AUTHOR EMAILID

="psmith@sfsu.edu">

<FNAME>smith</FNAME>

</AUTHOR>

<PAPER PAPERID = 10 EMAILID =

"sai@yahoo.com">

<MAINATHR>SHARMA</MAINATHR>

</PAPER>

<PAPER PAPERID = 10 EMAILID =

"sha@yahoo.com">

<MAINATHR>SHARMA</MAINATHR>

</PAPER>

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

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

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

return

<result

PAPERID="{$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 to

run 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/IP

Illustrated</title>

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

<publisher>Addison-Wesley</publisher>

</book>

<title>Advanced Programming in the

Unix 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 Kaufmann

Publishers</publisher>

</book>

<title>The Economics of Technology

and Content for Digital TV</title>

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

</editor>

<publisher>Kluwer Academic

Publishers</publisher>

</book>

</bib>

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

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