Xquery grouping question

Question

I have an XML database which I need to query. Below is a portion of the database.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<DVDStore>
<DVDTitles>
     <DVDTitle>
          <title>A. I. Artificial Intelligence </title>
          <date>2002-03-05</date>
          <studio>
               <name>Universal studios</name>
          </studio>
          <rated>PG-13</rated>
          <region_code>1</region_code>
          <directors>
               <name>Steven Spielberg</name>
          </directors>
          <starring>
               <name>Haley Joel Osment</name>
               <name>Jude Law</name>
          </starring>
          <reviews>
               <review>
                    <reviewer>
                         <name>Andrew</name>
                    </reviewer>
                    <review_date>2002-01-31</review_date>
                    <location>San Diego, CA</location>
                    <rating>5</rating>
                    <comment>Amazing, visually stunning and thought-inspiring</comment>
               </review>
####I can retrieve and calculate distinct titles with their average rating.
<studios>
for $s in distinct-values(//studio/name)
let $title := //DVDTitles/DVDTitle
order by $s
return <studio><name>{$s}</name><DVDTitles>
for $t in $title
where $s=$t//studio
order by $t/title
return $t/title
}</DVDTitles></studio>
</studios>
####I can retrieve and list each title grouped by their studios.
<studios>
for $s in distinct-values(//studio/name)
let $title := //DVDTitles/DVDTitle
order by $s
return <studio><name>{$s}</name><DVDTitles>
for $t in $title
where $s=$t//studio
order by $t/title
return $t/title
}</DVDTitles></studio>
</studios>
I can't seem to get the distinct titles with their average ratings group by their studios.
Can anyone help?

Answer 1

You've given twice the same query...
Do you really need to check for distinct titles in the database? Aren't they supposed to be unique?
How about :
let $d := doc("c:\temp\dvdstore.xml")
return
<studios>
  for $s in distinct-values($d//studio/name)
  order by $s
  return <studio>
     <name>{$s}</name>
     <titles>
         for $t in $d//DVDTitle
       where $t/studio/name = $s
         return <title>
          <name>{$t/title/text()}</name>
          <avg-rating>{avg($t/reviews/review/rating)}</avg-rating>
              </title>
     </titles>
         </studio>
</studios>If your processor supports XQuery 3.0 then you can use a group-by expression :
let $d := doc("c:\temp\dvdstore.xml")
return
<studios>
  for $t in $d//DVDTitle
  let $s := $t/studio/name
  let $title := <title>
            <name>{$t/title/text()}</name>
                 <avg-rating>{avg($t/reviews/review/rating)}</avg-rating>
                </title>
  group by $s
  order by $s
  return <studio>
     <name>{$s/text()}</name>
     <titles>{$title}</titles>
         </studio>
</studios>