如何从 XQuery 中的重复节点中检索最大值？答案

【问题标题】：How to retrieve largest value from duplicate nodes in XQuery?如何从 XQuery 中的重复节点中检索最大值？
【发布时间】：2020-02-10 19:58:29
【问题描述】：

我有一个 XML 文件。我想从重复值中检索最大值节点（在下面的例子中，author、title 和genre 字段相同，但number 字段不同）。

<?xml version="1.0"?>
<catalog>
   <book>
      <author>Gambardella, Matthew</author>
      <title>XML Developer's Guide</title>
      <genre>Computer</genre>
      <number>1234</number>
   </book>
   <book>
      <author>Ralls, Kim</author>
      <title>Midnight Rain</title>
      <genre>Fantasy</genre>
      <number>1235</number>
   </book>
   <book>
      <author>Corets, Eva</author>
      <title>Maeve Ascendant</title>
      <genre>Fantasy</genre>
      <number>1236</number>
   </book>
   <book>
      <author>Corets, Eva</author>
      <title>Oberon's Legacy</title>
      <genre>Fantasy</genre>
      <number>1237</number>
   </book>
   <book>
      <author>Corets, Eva</author>
      <title>The Sundered Grail</title>
      <genre>Fantasy</genre>
      <number>1238</number>
   </book>
   <book>
      <author>Randall, Cynthia</author>
      <title>Lover Birds</title>
      <genre>Romance</genre>
      <number>1239</number>
   </book>
   <book>
      <author>Thurman, Paula</author>
      <title>Splish Splash</title>
      <genre>Romance</genre>
      <number>1240</number>
   </book>
   <book>
      <author>Thurman, Paula</author>
      <title>Splish Splash</title>
      <genre>Romance</genre>
      <number>1246</number>
   </book>
   <book>
      <author>Thurman, Paula</author>
      <title>Splish Splash</title>
      <genre>Romance</genre>
      <number>1247</number>
   </book>
   <book>
      <author>Thurman, Paula</author>
      <title>Splish Splash</title>
      <genre>Romance</genre>
      <number>1248</number>
   </book>
   <book>
      <author>Knorr, Stefan</author>
      <title>Creepy Crawlies</title>
      <genre>Horror</genre>
      <number>1241</number>
   </book>
   <book>
      <author>Kress, Peter</author>
      <title>Paradox Lost</title>
      <genre>Science Fiction</genre>
      <number>1242</number>
   </book>
   <book>
      <author>O'Brien, Tim</author>
      <title>Microsoft .NET: The Programming Bible</title>
      <genre>Computer</genre>
      <number>1243</number>
   </book>
   <book>
      <author>O'Brien, Tim</author>
      <title>MSXML3: A Comprehensive Guide</title>
      <genre>Computer</genre>
      <number>1244</number>
   </book>
   <book>
      <author>Galos, Mike</author>
      <title>Visual Studio 7: A Comprehensive Guide</title>
      <genre>Computer</genre>
     <number>1245</number>
   </book>
</catalog>

这是预期的输出：

<?xml version="1.0"?>
<catalog>
   <book>
      <author>Gambardella, Matthew</author>
      <title>XML Developer's Guide</title>
      <genre>Computer</genre>
      <number>1234</number>
   </book>
   <book>
      <author>Ralls, Kim</author>
      <title>Midnight Rain</title>
      <genre>Fantasy</genre>
      <number>1235</number>
   </book>
   <book>
      <author>Corets, Eva</author>
      <title>Maeve Ascendant</title>
      <genre>Fantasy</genre>
      <number>1236</number>
   </book>
   <book>
      <author>Corets, Eva</author>
      <title>Oberon's Legacy</title>
      <genre>Fantasy</genre>
      <number>1237</number>
   </book>
   <book>
      <author>Corets, Eva</author>
      <title>The Sundered Grail</title>
      <genre>Fantasy</genre>
      <number>1238</number>
   </book>
   <book>
      <author>Randall, Cynthia</author>
      <title>Lover Birds</title>
      <genre>Romance</genre>
      <number>1239</number>
   </book>
   <book>
      <author>Thurman, Paula</author>
      <title>Splish Splash</title>
      <genre>Romance</genre>
      <number>1248</number>
   </book>
   <book>
      <author>Knorr, Stefan</author>
      <title>Creepy Crawlies</title>
      <genre>Horror</genre>
      <number>1241</number>
   </book>
   <book>
      <author>Kress, Peter</author>
      <title>Paradox Lost</title>
      <genre>Science Fiction</genre>
      <number>1242</number>
   </book>
   <book>
      <author>O'Brien, Tim</author>
      <title>Microsoft .NET: The Programming Bible</title>
      <genre>Computer</genre>
      <number>1243</number>
   </book>
   <book>
      <author>O'Brien, Tim</author>
      <title>MSXML3: A Comprehensive Guide</title>
      <genre>Computer</genre>
      <number>1244</number>
   </book>
   <book>
      <author>Galos, Mike</author>
      <title>Visual Studio 7: A Comprehensive Guide</title>
      <genre>Computer</genre>
     <number>1245</number>
   </book>
</catalog>

作者在哪里Thurman, Paula。应检索最大数量的节点。有什么方法可以检索输出吗？如果是这样，请指导我正确的方向。

提前致谢！！

【问题讨论】：

标签： xml xquery xquery-3.0

【解决方案1】：

您可以按包含所有重复值（作者、标题、流派）的字符串对您的书籍进行分组，并返回该组中具有最大数量的书籍：

element catalog {
  for $book-group in catalog/book
  group by $key := string-join($book-group/(author, title, genre), '|')
  let $max-number := max($book-group/number)
  return $book-group[number = $max-number]
}

【讨论】：