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Re: isNumeric

From: Steve Harris <steve.harris@garlik.com>
Date: Mon, 27 Sep 2010 15:49:49 +0100
Cc: "Polleres, Axel" <axel.polleres@deri.org>, public-rdf-dawg@w3.org
Message-Id: <2260FE10-9A40-4841-81D7-FFEDB9C7A2D1@garlik.com>
To: Andy Seaborne <andy.seaborne@epimorphics.com>
The situation is much less murky in SQL as columns are typed, so SUM(x) => "1"^^xsd:integer + "foo" doesn't really arise.

- Steve
 
On 2010-09-27, at 15:04, Andy Seaborne wrote:

> In SQL, what's being aggregated is statically typed and may involve implicit conversion.
> 
>   SQL standard requires nulls to be skipped in SUM.
>   MySQL skips errors just like NULLs.
>   PostgreSQL skips nulls and expression errors on sum(val+5)
>   PostgreSQL causes an error on casting error.
>   Addition with + and nulls does not work as sum over nulls.
> 
> 
> 3/ SQL92 defines sum in language, the core of which seems to be:
> 
> [[
> If SUM is specified, then the result is the sum of the
>                 values in TXA.
> ]]
> 
> [1]
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2009OctDec/0433.html
> 
> 	Andy
> 
> On 27/09/10 13:43, Polleres, Axel wrote:
>> How does SQL deal with that?
>> 
>> Axel
>> 
>> ----- Original Message -----
>> From: Steve Harris<steve.harris@garlik.com>
>> To: Polleres, Axel
>> Cc: Andy Seaborne<andy.seaborne@epimorphics.com>; SPARQL Working Group<public-rdf-dawg@w3.org>
>> Sent: Mon Sep 27 12:43:58 2010
>> Subject: Re: isNumeric
>> 
>> On 2010-09-20, at 09:55, Axel Polleres wrote:
>> 
>>> On 20 Sep 2010, at 10:26, Andy Seaborne wrote:
>>>> On 19/09/10 21:13, Axel Polleres wrote:
>>>>> Hi all,
>>>>> 
>>>>> Don't we need something like a function isNumeric to test for a numeric argument?
>>>>> Seems to be handy, useful for instance for numeric aggregates, or no?
>>>>> 
>>>>> It seems COALESCE together with a cast would work as well, but
>>>>> something like
>>>>>   SUM(IF(isNumeric(?X), ?X, 0))
>>>>> looks better - at least to me - than:
>>>>>     SUM(COALESCE(xs:double(?X) , 0))
>>>>> 
>>>>> Opinions?
>>>>> 
>>>>> Axel
>>>> 
>>>> I believe we eventually agreed that sum() would skip any evaluation
>>>> errors of the summation as being more consistent in style for SPARQL.
>>> 
>>> Hmmm, I read up in the F2F minutes
>>> http://www.w3.org/2009/sparql/meeting/2010-03-26#SUM
>>> and couldn't find it there... according to the current definition SUM just delegates to op:numeric-add
>>> which would error on non-numeric values, wouldn't it?
>>> 
>>> Note that Resolution http://www.w3.org/2009/sparql/meeting/2010-03-26#resolution_2
>>> doesn't cover that, since the argument passed is not an error, but just
>>> the wrong datatype.
>>> 
>>> We might have that resolved otherwise somewhere, but frankly I can't find that.
>> 
>> My recollection matches Axels, but I don't have a clear memory of the discussions. I would expect to have to do a cast and/or coalesce to protect from type errors.
>> 
>> - Steve
>> 
> 

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Received on Monday, 27 September 2010 15:23:46 GMT

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