Question

这是DTD

<!ELEMENT Responses (Student*)>

<!ELEMENT Student (Response+)>

    <!ATTLIST Student   studentID ID #REQUIRED>



<!ELEMENT Response (List+)>

<!ELEMENT List (#PCDATA)>

    <!ATTLIST List questionID IDREF #REQUIRED>

我想要大多数学生所在的大学。如果有领带，请报告所有并列的大学。

let $student := doc("responses.xml")/Responses/Student 

for $dc in distinct-values 
    (for $college in $student/Response/List[@questionID = "college"]
    return data($college))

return <College>{$dc} - number of students: {count($student[Response/List[@questionID = "college"] = data($dc)])</College>)

我在count（）时遇到错误，我只想用条件计算。

第二个问题如何选择最大值

Answer 1

代码的最后一行有一个拼写错误。在计数之前你有一个开放的花括号，但它在</College>之前没有关闭，并且在</College>之后还有一个额外的右括号。

要获得与大多数学生相关的大学（由？参加），您需要在计数上订购，并获取以该方式返回的第一个项目。请参阅下面稍作修改的代码。

注意：我不得不猜测一下你的数据，所以我自己创造了一些东西。事实上，实际上有三所大学具有相同的最大值，但只返回一个。你可能想稍微调整一下，首先找到最大数量本身，然后使用它来查找所有具有该数量的大学...

let $doc := 
    document {
        <Responses>
            <Student studentID="s1">
                <Response>
                    <List questionID="college">q1</List>
                    <List questionID="college">q2</List>
                    <List questionID="college">q3</List>
                </Response>
                <Response>
                    <List questionID="college">q4</List>
                    <List questionID="college">q5</List>
                    <List questionID="college">q6</List>
                </Response>
            </Student>
            <Student studentID="s2">
                <Response>
                    <List questionID="college">q4</List>
                    <List questionID="college">q5</List>
                    <List questionID="college">q6</List>
                </Response>
                <Response>
                    <List questionID="college">q7</List>
                    <List questionID="college">q8</List>
                    <List questionID="college">q9</List>
                </Response>
            </Student>
            <Student studentID="s3">
                <Response>
                    <List questionID="college">q1</List>
                    <List questionID="college">q2</List>
                    <List questionID="college">q3</List>
                </Response>
                <Response>
                    <List questionID="college">q4</List>
                    <List questionID="college">q5</List>
                    <List questionID="college">q6</List>
                </Response>
            </Student>
        </Responses>
    }

let $student := $doc/Responses/Student
return (
    for $dc in
        distinct-values(
            for $college in $student/Response/List[@questionID = "college"]
            return data($college)
        )
    let $count := count($student[Response/List[@questionID = "college"] = data($dc)])
    order by $count descending, $dc ascending
    return <College>{$dc} - number of students: {$count}</College>
)[1]

Xquery计算条件

1 个答案: