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Re: rq25 aggregate functions

From: Steve Harris <steve.harris@garlik.com>
Date: Mon, 21 Dec 2009 23:48:51 +0000
Cc: "public-rdf-dawg@w3.org Group" <public-rdf-dawg@w3.org>
Message-Id: <B1750CAF-C65A-4460-B960-998F102EBA99@garlik.com>
To: Andy Seaborne <andy.seaborne@talis.com>
On 21 Dec 2009, at 18:10, Andy Seaborne wrote:
> On 20/12/2009 19:59, Steve Harris wrote:
>> Hi all,
>>
>> I've just added the text on aggregate functions to
>> http://www.w3.org/2009/sparql/docs/query-1.1/rq25.xml#aggregateFunctions
>>
>> The main new content is a new definition of Aggregation, to match the
>> groups intentions for the use of aggregate functions, and definitions
>> for COUNT, SUM, MIN, MAX, AVG, GROUP_CONCAT, and SAMPLE.
>>
>> The notation around “exp · μ'” in Aggregation is questionable,  
>> so if
>> anyone has a better suggestion I'm all ears.
>>
>> I'm hoping to put the definitions for sub-select in rq25 on Monday.
>>
>> - Steve
>>
>
> [[
> Definition: GroupConcat
>
> The multiset of values passed as an argument is converted to a  
> sequence S.
>
> GroupConcat(S) = fn:string-join(S, " ")
>
> @@ do we want space as the seperator? It's annoying in names for  
> example. Other reasonable choices include ",", "\n", or "\t".
> ]]
>
> All reasonable, none always right. I suggest that GroupConcat take  
> an optional separator defaulting to a single space.
>
> If the elements are "a" "b" "c"
>
> CONCAT(?x) -> "a b c"
> CONCAT(?x, "/") -> "a/b/c"
>
> If the elements are integers 1 2 3
>
> CONCAT(str(?x)+1) -> "2 3 4"
> CONCAT(str(?x)+1, "+") -> "2+3+4"

I did consider that, but it conflicts with the semantics of aggregates  
(both in SQL, and what's currently in the SPARQL draft).

One option would be a keyword, like GROUP_CONCAT(str(?x) SEPARATOR  
"+"), this is what MySQL does, but it means some special case syntax.

- Steve
Received on Monday, 21 December 2009 23:49:32 GMT

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