Question

I am supposed to write an XQuery based SQL script to merge data from 3 different XML files into one unified format
.
The output should be of the following format:

<Courses>
<Course school="NYU">
<Number>30144</Number>
<Title>C‐PAC II</Title>
<Instructor>Lewis</Instructor>
</Course>
...
<Course school="Harvard">
<Number>4949</Number>
<Title>Computer Science 50. Introduction to Computer Science I</Title>
<Instructor>Michael D. Smith</Instructor>
</Course>
...
</Courses>

I had written the following script to achieve the above:

SELECT catalog.query('
<Courses>
{
(<Course school = "NYU">
{
for $x in (/nyu/Course)
return 
<Number> {$x/CallNo/text()} </Number>
<Title> {$x/Name/text()} </Title>
<Instructor> {$x/Instructor/text()} </Instructor>
}
</Course>)

union       

(<Course school = "Harvard">
{
for $y in (/harvard/Course)
return
<Number> {$y/Number/text()} </Number>
<Title> {$y/Title/text()} </Title>
<Instructor> {$y/Instructor/text()} </Instructor>
}               
</Course>)

union

(<Course scool = "Umich">
{
for $z in (/umich/Course)
return
<Number> {$z/@catalognumber} </Number>
<Title> {$z/name/text()} </Title>
}
</Course>)
}                       
</Courses>
')      
from catalogs

Can anyone please tell me where I have went wrong?

Answer 1

XQuery operators work with sequences of nodes, not files. The syntax would be something like this:

document("umich.xml")/umich/Course UNION document("harvard.xml")/harvard/Course UNION document("nyu.xml")/nyu/Course

Use the document function to return nodes from files, and the union operator to create the result set.