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Re: [xsl] following-sibling is evil


Subject: Re: [xsl] following-sibling is evil
From: "Dimitre Novatchev dnovatchev@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Sun, 6 Jul 2014 20:42:58 -0000

On Sun, Jul 6, 2014 at 12:39 PM, Michael Kay mike@xxxxxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>>    following-sibling::Book[Title eq $currentAuthor and Genre eq
>> $currentGenre][1]
>
> I can't see why that's obviously more efficient. They look identical to me.

The "naive" processor will perform only one and not two passes --
doing both comparisons in a single pass.


>>
>> or probably even better (as a hint to the optimizer):
>>
>>    exists(head(following-sibling::Book[Title eq $currentAuthor and
>> Genre eq $currentGenre]))
>
> Again, it's still quadratic performance if your evaluate this for every Book.

Yes, "more efficient" here is relative to the initial expression, not
in big O terms.

>>




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


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