Question

我有两个XML文档Students.xml和Admission.xml，我需要一个xquery来返回从录取日期起30天内完成学生的学生ID和学生姓名。我很困惑如何加入他们并使用条件来提出，请帮忙。

Student.xml

<?xml version="1.0" encoding="UTF-8" ?>
<root>
<StudentDetails>
    <Student_ID>1</Student_ID>
    <Student_Name>Mark</Student_Name>
</StudentDetails>
<StudentDetails>
    <Student_ID>2</Student_ID>
    <Student_Name>Robin</Student_Name>
</StudentDetails>
<StudentDetails>
    <Student_ID>3</Student_ID>
    <Student_Name>Charlie</Student_Name>
</StudentDetails>
</root>

Admission.xml

<?xml version="1.0" encoding="UTF-8" ?>
<root>
<AdmissionDetails>
    <Admission_ID>1</Admission_ID>
    <Admission_Date>2017-10-06</Admission_Date>
    <Admission_Status>Admitted</Admission_Status>
    <Student_ID>3</Student_ID>
</AdmissionDetails>
<AdmissionDetails>
    <Admission_ID>2</Admission_ID>
    <Admission_Date>2017-04-14</Admission_Date>
    <Admission_Status>Admitted</Admission_Status>
    <Student_ID>2</Student_ID>
</AdmissionDetails>
<AdmissionDetails>
    <Admission_ID>3</Admission_ID>
    <Admission_Date>2017-08-16</Admission_Date>
    <Admission_Status>Admitted</Admission_Status>
    <Student_ID>1</Student_ID>
</AdmissionDetails>

到目前为止，我的代码是这样的，但它给了我一个重复值的结果，拼命地需要帮助。

for $sid in doc("Student.xml")/root/StudentDetails/Student_ID
for $aid  in doc("Admission.xml")/root/AdmissionDetails/Student_ID
for $x in doc("Admission,xml")/root/AdmissionDetails/Admission_Date
where $sid = $aid and $x >current-date() + xs:dayTimeDuration("P30D")
return  $sid

这是结果

<?xml version="1.0" encoding="UTF-8"?>
<Student_ID>1</Student_ID>
<Student_ID>1</Student_ID>
<Student_ID>10</Student_ID>
<Student_ID>10</Student_ID>

Answer 1

我认为你陷入了这样的陷阱，即每个查询都必须是一个FLWOR表达式（它通常表明你花了太长时间编写SQL）。

我会把它写成：

    let $S30 := doc("Admission.xml")/*/Admission_Details
        [xs:date(Admission_Date) < current-date() + xs:dayTimeDuration("P30D")]
        /Admission_ID
    return doc("Student.xml")/*/StudentDetails[Student_ID = $S30]

Answer 2

您可以迭代Students.xml文档中的每个StudentDetails，然后过滤WHERE StudentDetails/Student_ID值等于Admission.xml AdmissionDetails元素的Student_ID并且Admission_Date符合您的条件（您确定这是正确的日期过滤器吗？您的说明是在入学后30天内说明完成日期，但样本数据没有完成日期，仅入学日期），然后从满足WHERE子句条件的学生那里返回Student_ID和Student_Name。

for $student in doc("Student.xml")/root/StudentDetails
where doc("Admission.xml")/root/AdmissionDetails[
        Student_ID = $student/Student_ID and 
        xs:date(Admission_Date) < current-date() + xs:dayTimeDuration("P30D") 
      ]
return 
  ($student/Student_ID, $student/Student_Name)

XQuery规范中包含可能提供信息的“内部”和“外部”joins的示例。

在两个XML文档上使用if语句

2 个答案: