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Re: [xsl] Which is faster: count(/Document/A/B) eq 1 ... or ... /Document/A/(count(B) eq 1) ?


Subject: Re: [xsl] Which is faster: count(/Document/A/B) eq 1 ... or ... /Document/A/(count(B) eq 1) ?
From: Dimitre Novatchev <dnovatchev@xxxxxxxxx>
Date: Wed, 19 Sep 2012 07:24:24 -0700

/*/*/b[1][not(following-sibling::b)]

Cheers,
Dimitre

On Wed, Sep 19, 2012 at 7:07 AM, David Carlisle <davidc@xxxxxxxxx> wrote:
> On 19/09/2012 14:34, Costello, Roger L. wrote:
>>
>> Is there an XPath expression, besides the ones listed, that is even better
>> and faster?
>
>
>
> You want to avoid count() as then you are relying on the optimiser to
> rewrite it away. If you go count(B) eq 1 then unless the optimiser spots
> this it may try to calculate count(B) which would mean processing the full
> list of elements.
>
> B and not(B[2])
>
> similarly may be read as evaluating the full list of B elements and then
> taking the 2nd but it is much more likely the optimiser detects [2]
> predicates to abort the construction of the sequence at the second item.
>
> David
>
>
> --
> google plus: https:/profiles.google.com/d.p.carlisle
>
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-- 
Cheers,
Dimitre Novatchev
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