xquery 读书笔记

xquery使用函数从xml文档中提取数据。doc()函数用来打开文档
doc(“books.xml“)
eg:
doc("books.xml")/bookstore/book/title 
doc("books.xml")/bookstore/book[price<30]

FLWOR表达式 For, Let, Where, Order by, Return

for $x in doc("books.xml")/bookstore/book
where $x/price>30
return $x/title
其效果等同于doc("books.xml")/bookstore/book[price<30]
添加排序功能：

for $x in doc("books.xml")/bookstore/book
where $x/price>30
order by $x/title
return $x/title
比较运算符

1. General comparisons: =, !=, <, <=, >, >=
2. Value comparisons: eq, ne, lt, le, gt, ge

for子句：循环指定次数 for $x in (1 to 5)
         利用at计算循环次数 for $x at $i in doc("books.xml")/bookstore/book/title

         循环嵌套 for $x in (10,20), $y in (100,200) 
                    return <test>x={$x} and y={$y}</test>

                   $y是内循环，参考结果：
                    <test>x=10 and y=100</test>
                    <test>x=10 and y=200</test>
                    <test>x=20 and y=100</test>
                    <test>x=20 and y=200</test>
let子句：不进行循环
                    let $x := (1 to 5)
                    return <test>{$x}</test>
                    结果： <test>1 2 3 4 5</test>   
where子句：指定过滤条件
                    where $x/price>30 and $x/price<100
order by 子句：指定结果的排序

                    for $x in doc("books.xml")/bookstore/book
                    order by $x/@category, $x/title
                    return $x/title
                    结果：              
                    <title lang="en">Harry Potter</title>
                    <title lang="en">Everyday Italian</title>
                    <title lang="en">Learning XML</title>
                    <title lang="en">XQuery Kick Start</title>
return子句： 返回结果
xquery函数介绍页面（w3school提供）




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