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Re: ungrouped variables used in projections - Further implications?

From: Steve Harris <steve.harris@garlik.com>
Date: Fri, 27 Aug 2010 13:29:13 +0100
Cc: "Andy Seaborne" <andy.seaborne@epimorphics.com>, "SPARQL Working Group" <public-rdf-dawg@w3.org>, "Lee Feigenbaum" <lee@thefigtrees.net>
Message-Id: <F84D20A3-59BA-4C11-B074-A26A068FB497@garlik.com>
To: Axel Polleres <axel.polleres@deri.org>
On 2010-08-26, at 15:46, Axel Polleres wrote:
...
>> It's a restriction but I don't see it as /very/ restricting, especially
>> as you have already shown that if the app needs the value of the
>> grouping returned it can do so using a nested SELECT.
>> 
>> The balance is the difficulty of determining whether one expression is a
>> sub-expression of another, including reordering and rewriting.
>> 
>> Consider
>> 
>> GROUP BY (1/?o)
>> 
>> then
>> 
>> SELECT (fn:floor(1/(-2*?o))+count(*)))
> 
> Sure, but I had maent to allow only the *exact same* expression as the 
> grouped expression as subexpression.

That will be very hard to detect reliably. Bear in mind the expression will have been through a parser by this point, and not all parsers will implement identical grammars (e.g. different kinds of parser, syntax extensions, and so on).

- Steve

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Received on Friday, 27 August 2010 12:29:48 GMT

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