[xquery-talk] group by queries - a more efficient approach

[Dmitri.Colebatch at toyota.com.au]

hey again,

hope that I'm not imposing too much on this list... definately making
progress, would like some thoughts on group by style queries...  Suppose I
have this document:

<mydata>
      <book>
            <name>Struts</name>
            <subject>Java</subject>
      </book>
      <book>
            <name>EJB</name>
            <subject>Java</subject>
      </book>
      <book>
            <name>Patterns</name>
            <subject>Design</subject>
      </book>
      <book>
            <name>Refactoring</name>
            <subject>Design</subject>
      </book>
      <book>
            <name>XSLT</name>
            <subject>XML</subject>
      </book>
</mydata>

and I want to create multiple documents (nodes), grouped by subject - I
couldn't find any mention of any support for group by queries, so I've used
the following:

for $s in distinct-values($this/mydata/book/subject)
return
      <books-by-subject>
      {
            for $book in $this/mydata/book[subject/text() = $s/text()]
                  return
                        <book>
                              <name>{$book/name}</name>
                              <subject>{$book/subject}</subject>
                        </book>
      }
      </books-by-subject>

which works, but "feels" like there might be a better approach...  has
anyone here done this sort of thing before?  any ideas?

the reason I'm doing this is that I'm receiving a document in batch mode
that has address information contained in its items - each item might go to
a different destination, so I want to "re-batch" the document into smaller
documents to be sent to their final destination.

cheers, and thanks again
dim

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