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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: David Carlisle <davidc@xxxxxxxxx>
Date: Wed, 19 Sep 2012 15:07:11 +0100

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.


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