How to count specific Attribute value using XQuery?

Question

Below is the XML File -

<Title t="1">
    <Book sub="Computers"/>
    <Book sub="Engg."/>
</Title>
<Title t="2">
    <Book sub="Computers"/>
</Title>
<Title t="1">
    <Book sub="Computers"/>
    <Book sub="Engg."/>
    <Book sub="Medical"/>
</Title>

What will be the XQuery to count the occurrences of "Computers"?

Answer 1

计算将'Computers'作为值的所有sub属性：

count(//@sub[. = 'Computers'])

Answer 2

Assuming that the provided XML fragment is wrapped in a single top element so that this becomes a well-formed XML document, then the following XPath expression (not using // ):

count(/*/*/*/@sub[. = 'Computers'])

produces the wanted result.