内的XQuery计数器 [英] XQuery counters inside a for

问题描述

假设我有以下XQuery代码：

Let's say I have the XQuery code below:

   for $y in doc("file.xml")/A/B

        for $x in $y/C where $x/constraint1 != "-" and $x/constraint2 > 2.00
            do stuff 

我可以使用计数器来计算要输入多少代码在第二个for循环内？
我尝试过此操作：

Can I use a counter, to count how many my code will enter inside the second for loop? I tried this:

   for $y in doc("file.xml")/A/B
       let $i := 0
        for $x in $y/C where $x/constraint1 != "-" and $x/constraint2 > 2.00
            $i := $i + 1

但我遇到了编译错误。我还需要总结一些约束，例如：

but I got compile errors. I also I need to sum some constraints like this:

   for $y in doc("file.xml")/A/B
       let $i := 0
       let $sum := 0
        for $x in $y/C where $x/constraint1 != "-" and $x/constraint2 > 2.13
            $i := $i + 1
            $sum := $sum + $x/constraint2

但当然也没有用：（。

任何建议都会受到赞赏。
另外，您能建议吗

Any suggestions will be highly appreciated. Also, can you suggest a good book/tutorial/site for doing such stuff?

推荐答案

您并不经常需要它，但是如果您确实需要确实需要在XQuery 中用于表达式的计数器变量（类似于中的 position（） xsl：for-each ），您可以使用 at 变量

You don't need it very often, but if you really do need a counter variable inside an XQuery for expression (analogous to position() in an xsl:for-each) you can use an at variable

for $x at $pos in //item return
  <item position="{$pos}" value="{string($x)}"/>

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