如何在 XQuery 中使用 FLOWR 从这家书店退回第三本书? [英] how to return the third book from this bookstore using FLOWR in XQuery?

问题描述

如何退还这家书店的第三本书?

How can I return the third book from this bookstore?

declare context item := document{
<bookstore>

<book category="cooking">
  <title lang="en">Everyday Italian</title>
  <author>Giada De Laurentiis</author>
  <year>2005</year>
  <price>30.00</price>
</book>

<book category="children">
  <title lang="en">Harry Potter</title>
  <author>J K. Rowling</author>
  <year>2005</year>
  <price>29.99</price>
</book>

<book category="web">
  <title lang="en">XQuery Kick Start</title>
  <author>James McGovern</author>
  <author>Per Bothner</author>
  <author>Kurt Cagle</author>
  <author>James Linn</author>
  <author>Vaidyanathan Nagarajan</author>
  <year>2003</year>
  <price>49.99</price>
</book>

<book category="web" cover="paperback">
  <title lang="en">Learning XML</title>
  <author>Erik T. Ray</author>
  <year>2003</year>
  <price>39.95</price>
</book>

</bookstore>
};

let $date := current-date()
for $ctx in context
return $ctx/bookstore/book[3]

到目前为止，我只是得到一个空白结果:

so far I'm just getting a blank result:

PS C:\Users\thufir\Desktop\basex>PS C:\Users\thufir\Desktop\basex> basex contextDoc.xqPS C:\Users\thufir\Desktop\basex>

PS C:\Users\thufir\Desktop\basex> PS C:\Users\thufir\Desktop\basex> basex contextDoc.xq PS C:\Users\thufir\Desktop\basex>

推荐答案

您的问题标题说使用 FLWOR 表达式"，但 FLWOR 表达式对于这样一个简单的查询来说太过分了.

Your question title says "using a FLWOR expression", but FLWOR expressions are overkill for such a simple query.

@YitzhakKhabinsky 提供了正确答案:

@YitzhakKhabinsky has provided a correct answer:

for $ctx in ./bookstore/book[3] return $ctx

但是表达式 for $X in Y return $X 只是一种表示 Y 的冗长方式，所以这简化为

but the expression for $X in Y return $X is just a verbose way of saying Y, so this simplifies to

./bookstore/book[3]

或者更简单

bookstore/book[3]

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