求子元素的总数？

发布于 2024-12-05 11:37:30 字数 434 浏览 0 评论 0原文

<?xml version="1.0" encoding="UTF-8"?>
<root>
    <author>
        <name>A</name>
        <book>Book1</book>
        <book>Book2</book>
    </author>
    <author>
        <name>B</name>
        <age>45</age>
        <book>Book3</book>
    </author>       
</root>

如何编写 XQuery 来显示作者的书籍总数？

原文

<?xml version="1.0" encoding="UTF-8"?>
<root>
    <author>
        <name>A</name>
        <book>Book1</book>
        <book>Book2</book>
    </author>
    <author>
        <name>B</name>
        <age>45</age>
        <book>Book3</book>
    </author>       
</root>

How do I write a XQuery to display the total number of books by an author?

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陪你搞怪i 2024-12-12 11:37:30

一种方法是：

let $max-books = max(/root/author/count(book))
return /root/author[count(book) = $max-books]

它将返回所有撰写了最大数量书籍的作者。

作为一个衬垫，这可以简化为：

/root/author[count(book) = max(/root/author/count(book))]

另一种方法是：

(for $author in /root/author
 order by count($author/book) descending
 return $author/name)[1]

它将返回拥有最大书籍数量的作者。

One approach is:

let $max-books = max(/root/author/count(book))
return /root/author[count(book) = $max-books]

which will return all authors who have authored a maximum number of books.

As a one liner, this can be simplified to:

/root/author[count(book) = max(/root/author/count(book))]

Another way to do this is:

(for $author in /root/author
 order by count($author/book) descending
 return $author/name)[1]

which will return an author with the maximum number of books.

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你是年少的欢喜 2024-12-12 11:37:30

@Fox：你不应该用“作业”来标记这个问题吗？ ;-)

@Oliver Hallam：恕我直言，@Fox 希望列出每位作者以及该作者的书籍数量，而不是书籍数量最多的作者。

您的第一个查询

let $max-books = max(/root/author/count(book))
return /root/author[count(book) = $max-books]

包含语法错误。您应该使用“：=”而不是仅使用“=”。此外

@Fox：要找到解决方案，请查看 FLWOR 表达式。您可以使用“for”部分通过 XPath 表达式选择每个图书节点，并将每个节点绑定到 $book 变量。然后使用“let”部分定义两个变量（$authorName 和 $amountOfBooks），并使用 $book 作为“起点”。最后，使用“返回”部分定义生成的 XML 所需的输出格式。

@Fox: should you not tag this question with "homework"? ;-)

@Oliver Hallam: IMHO, @Fox wants to list each author together with the amount of books by that author and not the author with the highest amount of books.

Your first query

let $max-books = max(/root/author/count(book))
return /root/author[count(book) = $max-books]

Contains a syntax error. You should use ":=" instead of only "=". Furthermore

@Fox: to find the solution, have a look at FLWOR expressions. You can use the "for" part to select each of the book nodes with an XPath expression and bind each node to a $book variable. Then use the "let" part to define two variables ($authorName and $amountOfBooks) using the $book as "starting point". Last, use the "return" part to define the output format you need for the resulting XML.

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