解决XQuery学习难题专家分享实用技巧与常见问题解答让你少走弯路快速提升技能成为XML高手职场加分

引言

XQuery是一种用于查询XML数据的强大语言，它在处理大量XML数据时表现出色。随着XML在各种企业应用、内容管理系统和数据交换中的广泛使用，掌握XQuery已成为数据处理和集成领域的重要技能。然而，许多学习者在学习XQuery过程中遇到各种困难，从理解基本语法到掌握高级查询技巧。本文旨在解决这些难题，提供专家级的实用技巧和常见问题解答，帮助读者少走弯路，快速提升技能，成为真正的XML高手，为职场增添竞争力。

XQuery基础

什么是XQuery？

XQuery是一种用于从XML文档中提取和操作数据的查询语言，类似于SQL用于关系数据库。XQuery建立在XPath表达式之上，提供了更强大的查询、转换和构造功能。它由W3C制定标准，是目前处理XML数据最强大的工具之一。

XQuery的基本语法

XQuery查询通常由一个前序声明（prolog）和一个查询主体组成。前序声明可以包括命名空间声明、函数定义等，而查询主体则定义了要执行的实际查询。

(: 简单的XQuery示例 :) let $doc := doc("books.xml") return $doc/books/book[price > 30]/title

这个查询从”books.xml”文档中选取价格大于30的所有书籍的标题。

XQuery的主要用途

从XML文档中提取数据
转换和重组XML数据
对XML数据进行聚合和计算
与数据库系统交互，查询存储的XML数据
构建Web服务和内容管理系统

常见学习难题

理解XQuery与XPath的关系

许多学习者混淆XQuery和XPath。实际上，XPath是XQuery的基础，XQuery扩展了XPath的功能。XPath用于在XML文档中导航和选择节点，而XQuery提供了更丰富的查询、转换和构造功能。

示例：XPath与XQuery对比

(: XPath表达式 - 选择所有书籍的标题 :) doc("books.xml")/books/book/title (: 等效的XQuery表达式 :) for $title in doc("books.xml")/books/book/title return $title

处理复杂的FLWOR表达式

FLWOR（For, Let, Where, Order by, Return）是XQuery的核心，但初学者往往难以掌握其复杂用法。

示例：FLWOR表达式

(: FLWOR表达式示例 :) for $book in doc("books.xml")/books/book let $author := $book/author where $book/price > 20 order by $book/title return <book> {$book/title} <author>{$author}</author> </book>

这个查询遍历所有书籍，筛选价格大于20的书籍，按标题排序，并返回包含标题和作者的新XML结构。

理解XQuery的类型系统

XQuery有严格的类型系统，包括节点类型、原子类型等。理解这些类型及其转换对编写有效查询至关重要。

示例：类型转换

(: 类型转换示例 :) let $price as xs:string := "29.99" let $price-as-decimal := xs:decimal($price) let $discounted-price := $price-as-decimal * 0.9 return <price> <original>{$price}</original> <as-decimal>{$price-as-decimal}</as-decimal> <discounted>{$discounted-price}</discounted> </price>

掌握XQuery函数库

XQuery提供了丰富的内置函数库，但初学者往往不知道如何有效利用这些函数。

示例：使用内置函数

(: 使用内置函数示例 :) let $books := doc("books.xml")/books/book return <statistics> <total-books>{count($books)}</total-books> <average-price>{avg($books/price)}</average-price> <most-expensive>{max($books/price)}</most-expensive> <titles-containing-XML> { for $book in $books[contains(title, "XML")] return $book/title } </titles-containing-XML> </statistics>

实用技巧

从简单查询开始

学习XQuery时，应从简单的XPath表达式开始，逐步过渡到更复杂的XQuery查询。

示例：从简单到复杂

(: 步骤1: 简单XPath表达式 :) doc("books.xml")/books/book/title (: 步骤2: 添加简单条件 :) doc("books.xml")/books/book[price > 20]/title (: 步骤3: 转换为简单XQuery :) for $title in doc("books.xml")/books/book[price > 20]/title return $title (: 步骤4: 添加更多逻辑 :) for $book in doc("books.xml")/books/book where $book/price > 20 return <book-title> {$book/title} <price>{$book/price}</price> </book-title>

使用FLWOR表达式构建复杂查询

掌握FLWOR表达式是XQuery的关键。通过分解每个子句的功能，可以更容易地构建复杂查询。

示例：复杂FLWOR查询

(: 使用FLWOR计算每类书籍的平均价格和数量 :) for $category in distinct-values(doc("books.xml")/books/book/category) let $books-in-category := doc("books.xml")/books/book[category = $category] let $avg-price := avg($books-in-category/price) return <category name="{$category}"> <average-price>{$avg-price}</average-price> <book-count>{count($books-in-category)}</book-count> <books> { for $book in $books-in-category order by $book/price descending return <book> <title>{$book/title}</title> <price>{$book/price}</price> </book> } </books> </category>

利用XQuery的模块化特性

将常用功能封装为函数和模块，提高代码的可重用性和可维护性。

示例：创建和使用模块

(: 定义模块 - 保存为 bookUtils.xqy :) module namespace bookUtils = "http://example.com/bookUtils"; declare function bookUtils:discount($price as xs:decimal, $discount-rate as xs:decimal) as xs:decimal { $price * (1 - $discount-rate) }; declare function bookUtils:format-price($price as xs:decimal) as xs:string { concat("$", format-number($price, "###,###.00")) }; (: 使用模块 - 主查询 :) import module namespace bookUtils = "http://example.com/bookUtils" at "bookUtils.xqy"; for $book in doc("books.xml")/books/book let $discounted-price := bookUtils:discount($book/price, 0.1) return <book> {$book/title} <original-price>{bookUtils:format-price($book/price)}</original-price> <discounted-price>{bookUtils:format-price($discounted-price)}</discounted-price> </book>

实践数据转换

XQuery不仅用于查询，还可用于XML数据转换。练习将XML转换为HTML、JSON或其他格式。

示例：XML转HTML

(: 将XML书籍数据转换为HTML表格 :) let $books := doc("books.xml")/books/book return <html> <head> <title>Book List</title> <style> table {{ border-collapse: collapse; width: 100%; }} th, td {{ border: 1px solid #ddd; padding: 8px; text-align: left; }} th {{ background-color: #f2f2f2; }} tr:nth-child(even) {{ background-color: #f9f9f9; }} </style> </head> <body> <h1>Book List</h1> <table> <tr> <th>Title</th> <th>Author</th> <th>Category</th> <th>Price</th> </tr> { for $book in $books order by $book/title return <tr> <td>{$book/title/text()}</td> <td>{$book/author/text()}</td> <td>{$book/category/text()}</td> <td>{concat("$", $book/price)}</td> </tr> } </table> </body> </html>

使用XQuery调试工具

利用XQuery调试工具，如BaseX、eXist-db或氧气XML编辑器，可以帮助识别和解决查询中的问题。

调试技巧：

使用注释逐步测试查询的各个部分
利用fn:trace()函数输出中间结果
使用IDE的调试功能设置断点和变量监视

(: 使用trace函数调试 :) for $book in doc("books.xml")/books/book let $price := trace($book/price, "Price: ") where $price > 20 return trace( <book>{$book/title}</book>, "Processing book: " )

常见问题解答

如何处理命名空间？

命名空间是XML中的常见概念，但在XQuery中处理它们可能比较复杂。

解决方案：

(: 声明和使用命名空间 :) declare namespace ns = "http://example.com/ns"; declare namespace atom = "http://www.w3.org/2005/Atom"; (: 使用命名空间前缀查询元素 :) for $entry in doc("feed.xml")/atom:feed/atom:entry return <entry> <title>{$entry/atom:title/text()}</title> <id>{$entry/atom:id/text()}</id> </entry> (: 处理默认命名空间 :) declare default element namespace "http://example.com/default"; for $book in doc("books.xml")/books/book return $book/title

如何进行条件逻辑？

XQuery提供了if-then-else表达式进行条件判断。

解决方案：

(: 使用if-then-else表达式 :) for $book in doc("books.xml")/books/book return <book> {$book/title} <status> { if ($book/price > 50) then "Expensive" else if ($book/price > 20) then "Moderate" else "Affordable" } </status> <discount> { if ($book/category = "Technology") then 0.15 else if ($book/category = "Fiction") then 0.10 else 0.05 } </discount> </book>

如何处理日期和时间？

XQuery提供了丰富的日期和时间处理函数。

解决方案：

(: 处理日期和时间 :) let $current-date := current-date() let $current-time := current-time() let $current-datetime := current-dateTime() let $publication-date := xs:date("2023-01-15") let $days-since-publication := $current-date - $publication-date return <date-info> <current-date>{$current-date}</current-date> <current-time>{$current-time}</current-time> <current-datetime>{$current-datetime}</current-datetime> <publication-date>{$publication-date}</publication-date> <days-since-publication>{$days-since-publication div xs:dayTimeDuration('P1D')}</days-since-publication> <formatted-date>{format-date($current-date, "[D01] [MNn] [Y0001]")}</formatted-date> </date-info>

如何进行字符串操作？

XQuery提供了多种字符串处理函数。

解决方案：

(: 字符串操作示例 :) for $book in doc("books.xml")/books/book let $title := $book/title/text() return <book> <original-title>{$title}</original-title> <upper-title>{upper-case($title)}</upper-title> <lower-title>{lower-case($title)}</lower-title> <title-length>{string-length($title)}</title-length> <contains-XML>{contains($title, "XML")}</contains-XML> <starts-with-The>{starts-with($title, "The")}</starts-with-The> <ends-with-Query>{ends-with($title, "Query")}</ends-with-Query> <first-10-chars>{substring($title, 1, 10)}</first-10-chars> <title-words>{tokenize($title, " ")}</title-words> <normalized-title>{normalize-space($title)}</normalized-title> </book>

如何处理序列和聚合？

XQuery对序列和聚合操作提供了强大支持。

解决方案：

(: 序列和聚合操作示例 :) let $books := doc("books.xml")/books/book let $prices := $books/price let $categories := distinct-values($books/category) return <price-statistics> <min-price>{min($prices)}</min-price> <max-price>{max($prices)}</max-price> <avg-price>{avg($prices)}</avg-price> <sum-price>{sum($prices)}</sum-price> <book-count>{count($books)}</book-count> <categories> { for $category in $categories let $category-books := $books[category = $category] return <category name="{$category}"> <count>{count($category-books)}</count> <avg-price>{avg($category-books/price)}</avg-price> </category> } </categories> </price-statistics>

进阶学习路径

深入理解XQuery数据模型

学习XQuery数据模型的细节，包括节点类型、序列、原子值等概念。

关键概念：

节点类型：元素、属性、文本、文档、注释、处理指令等
序列：XQuery中的基本数据结构，可以包含零个或多个项
原子值：字符串、数字、布尔值、日期等非节点值
类型系统：类型检查、类型转换和类型提升

掌握高级查询技术

学习更高级的查询技术，如量化表达式、迭代器、窗口函数等。

示例：高级查询技术

(: 量化表达式示例 :) let $books := doc("books.xml")/books/book return <results> <all-expensive>{every $price in $books/price satisfies $price > 20}</all-expensive> <some-expensive>{some $price in $books/price satisfies $price > 50}</some-expensive> </results> (: 使用窗口函数进行排名 :) for $book at $position in doc("books.xml")/books/book order by $book/price descending return <book rank="{$position}"> {$book/title} <price>{$book/price}</price> </book> (: 使用递归函数处理层次结构 :) declare function local:sum-hierarchy($node as node()) as xs:decimal { let $direct-value := xs:decimal($node/@value) let $children-sum := sum(for $child in $node/node return local:sum-hierarchy($child)) return $direct-value + $children-sum }; let $root := doc("hierarchy.xml")/root return <total>{local:sum-hierarchy($root)}</total>

学习XQuery更新功能

了解XQuery更新功能，学习如何修改XML数据。

示例：XQuery更新操作

(: XQuery更新示例 - 修改价格 :) copy $doc := doc("books.xml") modify ( for $book in $doc/books/book[price < 10] return replace value of node $book/price with $book/price * 1.1 ) return $doc (: 添加新元素 :) copy $doc := doc("books.xml") modify ( for $book in $doc/books/book return insert node <discount>0.05</discount> after $book/price ) return $doc (: 删除节点 :) copy $doc := doc("books.xml") modify ( for $book in $doc/books/book[price < 5] return delete node $book ) return $doc (: 重命名元素 :) copy $doc := doc("books.xml") modify ( for $title in $doc//title return rename node $title as "book-title" ) return $doc

探索XQuery与数据库集成

学习如何将XQuery与数据库系统集成，如BaseX、eXist-db、MarkLogic等。

示例：与数据库集成

(: BaseX数据库操作示例 :) (: 创建数据库 :) db:create("mydb", "books.xml", "books.xml") (: 查询数据库 :) for $book in db:open("mydb")/books/book where $book/price > 20 return $book/title (: 添加文档到数据库 :) db:add("mydb", "newbooks.xml", "newbooks") (: 更新数据库中的数据 :) db:replace("mydb", "books.xml", <books> { for $book in doc("books.xml")/books/book return <book> {$book/*} <last-updated>{current-dateTime()}</last-updated> </book> } </books> ) (: 全文搜索 :) for $book in db:open("mydb")/books/book[ft:search(title, "XML")] return $book

实践项目驱动学习

通过实际项目练习XQuery技能，如构建XML数据处理管道、创建Web服务或开发内容管理系统。

项目示例：XML数据处理管道

(: 步骤1: 数据提取 - 从多个XML文件中提取数据 :) let $source-data := ( doc("orders1.xml")/orders/order, doc("orders2.xml")/orders/order ) (: 步骤2: 数据转换 - 转换为统一格式 :) let $transformed-data := for $order in $source-data return <order id="{$order/@id}"> <customer> <name>{$order/customer/name}</name> <email>{$order/customer/email}</email> </customer> <items> { for $item in $order/items/item return <item product-id="{$item/product-id}"> <quantity>{$item/quantity}</quantity> <unit-price>{$item/unit-price}</unit-price> <total>{$item/quantity * $item/unit-price}</total> </item> } </items> <order-date>{xs:date($order/date)}</order-date> <total-amount>{sum($order/items/item/(quantity * unit-price))}</total-amount> </order> (: 步骤3: 数据验证 - 验证转换后的数据 :) let $validation-errors := for $order in $transformed-data where empty($order/customer/name) or $order/total-amount <= 0 return <error order-id="{$order/@id}"> { if (empty($order/customer/name)) then "Missing customer name" else (), if ($order/total-amount <= 0) then "Invalid total amount" else () } </error> (: 步骤4: 数据聚合 - 生成汇总报告 :) let $summary := <summary> <total-orders>{count($transformed-data)}</total-orders> <total-revenue>{sum($transformed-data/total-amount)}</total-revenue> <orders-by-customer> { for $customer in distinct-values($transformed-data/customer/email) let $customer-orders := $transformed-data[customer/email = $customer] return <customer email="{$customer}"> <order-count>{count($customer-orders)}</order-count> <total-spent>{sum($customer-orders/total-amount)}</total-spent> </customer> } </orders-by-customer> <monthly-sales> { for $month in distinct-values(format-date($transformed-data/order-date, "[Y0001]-[M01]")) let $month-orders := $transformed-data[format-date(order-date, "[Y0001]-[M01]") = $month] return <month name="{$month}"> <order-count>{count($month-orders)}</order-count> <revenue>{sum($month-orders/total-amount)}</revenue> </month> } </monthly-sales> </summary> (: 步骤5: 输出结果 :) return <results> <validation> { if (empty($validation-errors)) then <status>All orders are valid</status> else $validation-errors } </validation> {$summary} <sample-orders> { for $order in subsequence($transformed-data, 1, 3) return $order } </sample-orders> </results>

职场应用

数据集成与转换

XQuery在数据集成和转换项目中非常有用，特别是在处理不同系统间的XML数据交换时。

示例：订单到发票转换

(: 数据转换示例 - 将订单XML转换为发票格式 :) let $order := doc("order.xml")/order return <invoice> <invoice-number>INV-{$order/@id}</invoice-number> <invoice-date>{current-date()}</invoice-date> <due-date>{current-date() + xs:dayTimeDuration("P30D")}</due-date> <customer> <name>{$order/customer/name}</name> <address>{$order/customer/address}</address> <contact>{$order/customer/contact}</contact> </customer> <items> { for $item in $order/items/item let $line-total := $item/quantity * $item/unit-price return <item> <product-id>{$item/product-id}</product-id> <description>{$item/description}</description> <quantity>{$item/quantity}</quantity> <unit-price>{$item/unit-price}</unit-price> <line-total>{$line-total}</line-total> </item> } </items> <subtotal>{sum($order/items/item/(quantity * unit-price))}</subtotal> <tax>{sum($order/items/item/(quantity * unit-price)) * 0.08}</tax> <total>{sum($order/items/item/(quantity * unit-price)) * 1.08}</total> <payment-terms>Net 30 days</payment-terms> </invoice>

内容管理系统

XQuery在内容管理系统中广泛应用，用于查询、组织和发布内容。

示例：内容管理系统查询

(: 内容管理系统查询示例 - 获取特定类别的文章并按发布日期排序 :) declare namespace cms = "http://example.com/cms"; let $articles := collection("/db/articles")//cms:article let $featured-articles := for $article in $articles where $article/cms:category = "Technology" and $article/cms:status = "published" order by xs:dateTime($article/cms:publishDate) descending return <article id="{$article/@id}"> <title>{$article/cms:title/text()}</title> <summary>{$article/cms:summary/text()}</summary> <author>{$article/cms:author/cms:name/text()}</author> <publish-date>{$article/cms:publishDate/text()}</publish-date> <tags> { for $tag in $article/cms:tags/cms:tag return <tag>{$tag/text()}</tag> } </tags> <related-articles> { let $current-tags := $article/cms:tags/cms:tag/text() for $related in $articles[cms:status = "published" and . != $article] let $score := count($related/cms:tags/cms:tag[. = $current-tags]) where $score > 0 order by $score descending return <article score="{$score}"> <title>{$related/cms:title/text()}</title> <id>{$related/@id}</id> </article> } </related-articles> </article> return <featured-articles category="Technology"> {$featured-articles[position() <= 5]} </featured-articles>

Web服务开发

使用XQuery开发RESTful Web服务，处理XML数据请求和响应。

示例：XQuery RESTful Web服务

(: 简单的XQuery Web服务示例 - 图书API :) import module namespace request = "http://exquery.org/ns/request"; import module namespace response = "http://exquery.org/ns/response"; let $method := request:method() let $path := request:path-info() let $accept := request:header("Accept") (: 处理GET请求 :) return if ($method = "GET") then if ($path = "/books") then (: 获取所有图书列表 :) let $books := doc("books.xml")/books/book return if (contains($accept, "application/json")) then (: 返回JSON格式 :) let $json := json:serialize( <json type="object"> <books type="array"> { for $book in $books return <_ type="object"> <id type="string">{$book/@id}</id> <title type="string">{$book/title/text()}</title> <author type="string">{$book/author/text()}</author> <price type="number">{$book/price/text()}</price> </_> } </books> </json> ) return ( response:header("Content-Type", "application/json"), $json ) else (: 返回XML格式 :) ( response:header("Content-Type", "application/xml"), <books> { for $book in $books return <book id="{$book/@id}"> <title>{$book/title}</title> <author>{$book/author}</author> <price>{$book/price}</price> </book> } </books> ) else if (matches($path, "/books/[^/]+$")) then (: 获取特定图书详情 :) let $book-id := tokenize($path, "/")[last()] let $book := doc("books.xml")/books/book[@id = $book-id] return if (exists($book)) then if (contains($accept, "application/json")) then (: 返回JSON格式 :) let $json := json:serialize( <_ type="object"> <id type="string">{$book/@id}</id> <title type="string">{$book/title/text()}</title> <author type="string">{$book/author/text()}</author> <category type="string">{$book/category/text()}</category> <price type="number">{$book/price/text()}</price> <isbn type="string">{$book/isbn/text()}</isbn> <description type="string">{$book/description/text()}</description> <publish-date type="string">{$book/publish-date/text()}</publish-date> </_> ) return ( response:header("Content-Type", "application/json"), $json ) else (: 返回XML格式 :) ( response:header("Content-Type", "application/xml"), <book id="{$book/@id}"> <title>{$book/title}</title> <author>{$book/author}</author> <category>{$book/category}</category> <price>{$book/price}</price> <isbn>{$book/isbn}</isbn> <description>{$book/description}</description> <publish-date>{$book/publish-date}</publish-date> </book> ) else (: 图书不存在 :) ( response:status-code(404), response:header("Content-Type", "text/plain"), "Book not found" ) else (: 无效路径 :) ( response:status-code(404), response:header("Content-Type", "text/plain"), "Resource not found" ) else (: 不支持的HTTP方法 :) ( response:status-code(405), response:header("Content-Type", "text/plain"), "Method not allowed" )

报表生成

使用XQuery从XML数据生成各种格式的报表，如HTML、PDF或Excel。

示例：销售报表生成

(: 销售报表生成示例 :) let $sales := doc("sales.xml")/sales/record let $sales-by-region := for $record in $sales group by $region := $record/region return <region name="{$region}"> <total-sales>{sum($record/amount)}</total-sales> <record-count>{count($record)}</record-count> <average-sale>{avg($record/amount)}</average-sale> <sales-by-product> { for $product in distinct-values($record/product) let $product-sales := $record[product = $product] return <product name="{$product}"> <units-sold>{sum($product-sales/quantity)}</units-sold> <revenue>{sum($product-sales/amount)}</revenue> </product> } </sales-by-product> </region> let $monthly-sales := for $month in distinct-values(format-date($sales/date, "[Y0001]-[M01]")) let $month-sales := $sales[format-date(date, "[Y0001]-[M01]") = $month] return <month name="{$month}"> <total-sales>{sum($month-sales/amount)}</total-sales> <record-count>{count($month-sales)}</record-count> </month> return <html> <head> <title>Sales Report</title> <style> table {{ border-collapse: collapse; width: 100%; margin-bottom: 20px; }} th, td {{ border: 1px solid #ddd; padding: 8px; text-align: left; }} th {{ background-color: #f2f2f2; }} .summary {{ font-weight: bold; background-color: #e6f2ff; }} .region-header {{ background-color: #f0f8ff; }} .product {{ margin-left: 20px; }} </style> </head> <body> <h1>Sales Report</h1> <h2>Executive Summary</h2> <table> <tr class="summary"> <th>Metric</th> <th>Value</th> </tr> <tr> <td>Total Revenue</td> <td>${format-number(sum($sales/amount), "###,###.00")}</td> </tr> <tr> <td>Total Records</td> <td>{count($sales)}</td> </tr> <tr> <td>Average Sale</td> <td>${format-number(avg($sales/amount), "###,###.00")}</td> </tr> </table> <h2>Sales by Region</h2> { for $region in $sales-by-region order by xs:decimal($region/total-sales) descending return <div> <h3>{$region/@name}</h3> <table> <tr class="region-header"> <th>Metric</th> <th>Value</th> </tr> <tr> <td>Total Sales</td> <td>${format-number($region/total-sales, "###,###.00")}</td> </tr> <tr> <td>Record Count</td> <td>{$region/record-count}</td> </tr> <tr> <td>Average Sale</td> <td>${format-number($region/average-sale, "###,###.00")}</td> </tr> </table> <h4 class="product">Sales by Product</h4> <table class="product"> <tr> <th>Product</th> <th>Units Sold</th> <th>Revenue</th> </tr> { for $product in $region/sales-by-product/product order by xs:decimal($product/revenue) descending return <tr> <td>{$product/@name}</td> <td>{$product/units-sold}</td> <td>${format-number($product/revenue, "###,###.00")}</td> </tr> } </table> </div> } <h2>Monthly Sales Trend</h2> <table> <tr> <th>Month</th> <th>Total Sales</th> <th>Record Count</th> </tr> { for $month in $monthly-sales order by $month/@name return <tr> <td>{$month/@name}</td> <td>${format-number($month/total-sales, "###,###.00")}</td> <td>{$month/record-count}</td> </tr> } </table> <p>Report generated on: {current-dateTime()}</p> </body> </html>

数据分析

XQuery可用于XML数据的分析和聚合，支持业务决策。

示例：客户行为分析

(: 客户行为分析示例 :) let $transactions := doc("transactions.xml")/transactions/transaction let $customers := distinct-values($transactions/customer-id) return <customer-analysis> <summary> <total-customers>{count($customers)}</total-customers> <total-transactions>{count($transactions)}</total-transactions> <total-revenue>{sum($transactions/amount)}</total-revenue> <avg-transaction-value>{avg($transactions/amount)}</avg-transaction-value> </summary> <customer-segments> <high-value-customers> { let $customer-spending := for $customer in $customers let $customer-transactions := $transactions[customer-id = $customer] let $total-spent := sum($customer-transactions/amount) let $transaction-count := count($customer-transactions) order by $total-spent descending return <customer id="{$customer}"> <total-spent>{$total-spent}</total-spent> <transaction-count>{$transaction-count}</transaction-count> <avg-transaction>{$total-spent div $transaction-count}</avg-transaction> <first-transaction>{min($customer-transactions/date)}</first-transaction> <last-transaction>{max($customer-transactions/date)}</last-transaction> </customer> return subsequence($customer-spending, 1, 10) } </high-value-customers> <at-risk-customers> { let $threshold-date := current-date() - xs:dayTimeDuration("P90D") for $customer in $customers let $customer-transactions := $transactions[customer-id = $customer] let $last-transaction := max($customer-transactions/date) where $last-transaction < $threshold-date and count($customer-transactions) > 2 order by $last-transaction return <customer id="{$customer}"> <last-transaction>{$last-transaction}</last-transaction> <days-since-inactive>{days-from-duration(current-date() - $last-transaction)}</days-since-inactive> <total-spent>{sum($customer-transactions/amount)}</total-spent> <transaction-count>{count($customer-transactions)}</transaction-count> </customer> } </at-risk-customers> <new-customers> { let $threshold-date := current-date() - xs:dayTimeDuration("P30D") for $customer in $customers let $customer-transactions := $transactions[customer-id = $customer] let $first-transaction := min($customer-transactions/date) where $first-transaction > $threshold-date order by $first-transaction descending return <customer id="{$customer}"> <first-transaction>{$first-transaction}</first-transaction> <total-spent>{sum($customer-transactions/amount)}</total-spent> <transaction-count>{count($customer-transactions)}</transaction-count> </customer> } </new-customers> </customer-segments> <product-analysis> { for $product in distinct-values($transactions/product-id) let $product-transactions := $transactions[product-id = $product] return <product id="{$product}"> <revenue>{sum($product-transactions/amount)}</revenue> <units-sold>{sum($product-transactions/quantity)}</units-sold> <transaction-count>{count($product-transactions)}</transaction-count> <unique-buyers>{count(distinct-values($product-transactions/customer-id))}</unique-buyers> <avg-quantity>{avg($product-transactions/quantity)}</avg-quantity> </product> } </product-analysis> <seasonal-trends> { for $year in distinct-values(format-date($transactions/date, "[Y0001]")) let $year-transactions := $transactions[format-date(date, "[Y0001]") = $year] return <year value="{$year}"> { for $quarter in (1 to 4) let $quarter-start := xs:date(concat($year, "-", if ($quarter = 1) then "01-01" else if ($quarter = 2) then "04-01" else if ($quarter = 3) then "07-01" else "10-01")) let $quarter-end := $quarter-start + xs:yearMonthDuration("P3M") - xs:dayTimeDuration("P1D") let $quarter-transactions := $year-transactions[date >= $quarter-start and date <= $quarter-end] return <quarter number="{$quarter}"> <revenue>{sum($quarter-transactions/amount)}</revenue> <transaction-count>{count($quarter-transactions)}</transaction-count> </quarter> } </year> } </seasonal-trends> </customer-analysis>