xpath - How to make a for loop work for xquery, in the context of 'contains'? -


if have books.xml file like

<books>     <book isbn="123">         <collections>             <collection c="1" />             <collection c="2" />             <collection c="3" />             <collection c="4" />         </collections>     </book>     <book isbn="234">         <collections>             <collection c="1" />             <collection c="2" />             <collection c="3" />             <collection c="5" />         </collections>     </book> </books>

i want return isbns both books belong same collections.

declare variable $doc := doc("books.xml"); <samecollections> {      $b1 in $doc/books/book     $b2 in $doc/books/book     $b1 << $b2 ,         every $p in $b1/collections/collection          satisfies $p in $b2/collections/collection     return      ... } </samecollections>

how make work? i've tried inserting loop inside loop, nothing worked, think i'm misunderstanding syntax of xquery. help?

ideally, xquery processor supports group by, answer simple:

for $b in $books/book let $colls-key := string-join($b/collections/collection/@c, '') group $colls-key return element grouped {     $b/@isbn/string() }

if collections aren't ordered in data, can order them before generating key:

let $colls-key :=    string-join(     $c in $collections/collection/@c     order $c     return $c)

without group by it's little messier. 

declare function local:key($collections){   string-join($collections/collection/@c, '') };  $key in distinct-values($doc/books/book/local:key(collections)) return element grouped {   $doc/books/book[local:key(collections) eq $key]/@isbn/string() }

depending on xquery processor may less efficient, it's not advisable large data sets. if performance issue, can optimizations available specific implementation.


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