Hello Constantine,
your query very much looks like you want to group by each <pii/>
element. Using XQuery 3.0 there even is a construct aimed at that and I
would guess it should also preserve memory. It is called group by and
you can find some more information at
https://docs.basex.org/wiki/XQuery_3.0#Group_By or in the spec.
It will look something like this:
for $x in /dataset/item/pii
let $val := $x/string()
where count($x) > 1
return <duplicate>{$val}</duplicate>
By the way, it looks you are using null like a NULL statement in other
languages. Such a statement does not exist in XQuery. You might want to
return an empty set () instead.
Cheers,
Dirk
On 09/04/14 13:37, Hondros, Constantine (ELS-AMS) wrote:
> I'm running out of memory (1.5 GB allocated) when querying for duplicate node
> values over a fairly flat XML database of approximately 450 MB.
>
> Can anyone suggest a more memory-efficient approach to framing this query
> than iterating over distinct-values as I do below? I'm hoping that there are
> some Basex tips and tricks to help out here.
>
> for $val in distinct-values(/dataset/item/pii)
> let $cnt := count(/dataset/item/pii[. = $val])
> return
> if ($cnt > 1) then
> <duplicate>{$val}</duplicate>
> else
> null
>
>
> Thanks in advance,
> Constantine
>
>
> ________________________________
>
> Elsevier B.V. Registered Office: Radarweg 29, 1043 NX Amsterdam, The
> Netherlands, Registration No. 33156677, Registered in The Netherlands.
>
--
Dirk Kirsten, BaseX GmbH, http://basex.org
|-- Firmensitz: Blarerstrasse 56, 78462 Konstanz
|-- Registergericht Freiburg, HRB: 708285, Geschäftsführer:
| Dr. Christian Grün, Dr. Alexander Holupirek, Michael Seiferle
`-- Phone: 0049 7531 28 28 676, Fax: 0049 7531 20 05 22
