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

/*/*/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
>
> ________________________________________________________________________
> The Numerical Algorithms Group Ltd is a company registered in England
> and Wales with company number 1249803. The registered office is:
> Wilkinson House, Jordan Hill Road, Oxford OX2 8DR, United Kingdom.
>
> This e-mail has been scanned for all viruses by Star. The service is
> powered by MessageLabs.
> ________________________________________________________________________
>



-- 
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
-------------------------------------
Never fight an inanimate object
-------------------------------------
To avoid situations in which you might make mistakes may be the
biggest mistake of all
------------------------------------
Quality means doing it right when no one is looking.
-------------------------------------
You've achieved success in your field when you don't know whether what
you're doing is work or play
-------------------------------------
Facts do not cease to exist because they are ignored.
-------------------------------------
Typing monkeys will write all Shakespeare's works in 200yrs.Will they
write all patents, too? :)
-------------------------------------
I finally figured out the only reason to be alive is to enjoy it.