XQuery: How to get a specific value out of a tag?

Question

Suppose we have this xml:

<question>
    <test id="1">
        <tag k="a" v="1"/>
        <tag k="a" v="2"/>
        <tag k="b" v="3"/>
    </test>
    <test id="2">
        <tag k="a" v="1"/>
        <tag k="a" v="4"/>
        <tag k="b" v="5"/>
    </test>
    <test id="3">
        <tag k="a" v="2"/>
        <tag k="a" v="6"/>
        <tag k="b" v="7"/>
    </test>
</question>

I would like to return all values v of test, if k = "a" AND v = "1", like this:

v="3"
v="5"

So far my approach:

for $i in //test
where ($i/tag[@k = 'a' and @v = '1'])
return $i/tag/@v

But this is not correct because thats the return:

v="1"
v="2"
v="3"
v="1"
v="4"
v="5"

Thank you for your help:)

Answer 1

You are probably looking for something like

for $i in //test
where  ($i/tag[@k = 'a'][@v="1"])
return $i/tag[@k="b"]/@v

Answer 2

Your criteria for selection was not exactly clear, but this returns what you expected:

for $i in //test
where $i/tag[@k = 'a' and @v = '1']
return $i/tag[not(@k = 'a' or @v = '1')]/@v

You could simplify and do this in a single XPath expression:

//test/tag[@k = 'a' and @v = '1']/tag[not(@k = 'a' or @v = '1')]/@v