XQuery query, using two xml documents

Question

Using Enrollment.xml and Person.xml documents, I'm trying to list the names of students who have all A's. The ID field in Person refers to the StudentID field in Enrollment. There is an entry in enrollment for every class that a person is enrolled in (not one entry per student)

I can't seem to figure out how to write the query

Enrollment.xml form- >

<Document>
  <Table>
    <StudentID>170815037</StudentID>
    <Grade>C</Grade>
  </Table>
  <Table>
    <StudentID>193847547</StudentID>
    <Grade>A</Grade>
  </Table>
</Document>

Person.xml form - >

<Document>
  <Table>
    <Name>Wee Fletcher</Name>
    <ID>115423723</ID>
  </Table>
</Document>

Heres is what im trying working on, and i cant get it to work

for $a in doc("proj3/Person.xml")/Document/Table/ID
where every $s in doc("proj3/Enrollment.xml")//Table[StudentID = $a]
          satisfies ($s/Grade = "A")
    return $a/Name;

Jens Erat · Accepted Answer · 2011-11-02 00:15:11Z

2

There's a minor problem: You set $a to doc("proj3/Person.xml")/Document/Table/ID, and later access $a/Name (which returns non-existant .../Table/ID/Name).

Change the assignment in your first line and the comparison in second (add /ID here) and your code will be fine:

for $a in doc("proj3/Person.xml")/Document/Table
where every $s in doc("proj3/Enrollment.xml")//Table[StudentID = $a/ID]
          satisfies ($s/Grade = "A")
    return $a/Name;

edited Nov 2, 2011 at 0:15

answered Nov 1, 2011 at 23:46

Jens Erat

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7 Comments

user446836 Over a year ago

i've added the homework tag, and posted what i have so far. any comments?

Jens Erat Over a year ago

Try either "where any" (think that's the only problem in your statement) or the join pattern I provided. Probably using join-pattern will lead to better optimization in query compilers as it is more general.

user446836 Over a year ago

wouldn't "where any" list students that have one or more A's? My query is looking for students that have ALL A's.

Jens Erat Over a year ago

You're totally right, misread that. Will change my answer in a minute, found your problem.

user446836 Over a year ago

My solution works except for one problem. There are people in the Person table that aren't students, such as Instructors and Mentors. These people are getting returned as well, even though they do NOT appear in the enrollment table.

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