ADQL MOD

[Patrick Dowler]

If a really clear definition is in the standard then users of
non-compliant back-end DB can/should/must write code to mangle
ADQL->SQL that returns the correct answer. That's always the case,
sometimes simple (change function name), sometimes tricky (change
function usage to operator usage), and in this case maybe swapping
arguments. In the ADQL standard is especially important than not in
cases where RDBMS are not consistent, it just isn't free for everyone.

my 2c,

Pat



On 6 July 2016 at 01:49, Marco Molinaro <molinaro at oats.inaf.it> wrote:
> Hi again,
> reporting Ger's comment on the  MOD function
>
> 2016-07-05 21:25 GMT+02:00 Ger van Diepen <diepen at astron.nl>:
>> Maybe it should be described what the remainder is in case x and/or y is
>> negative.
>> E.g.: x%y gives different results in C and Python for negative numbers.
>>
>> Cheers,
>> Ger
>
> I indeed think it is (R)DBMS implementation dependent, maybe one more
> point to check with Dave's Cosmopterix.
>
> A quick search in the SQL standard discussions online seems to point out
> that A%B=R is valid with R having the same sign as A and ABS(R) being
> smaller than ABS(B), plus the counter check that A=B*K+R where K is some
> integer value (out of A/B).
>
> Maybe we are lucky and all the RDBMSs we're interested in act this way.
>
> I'm not sure, however, that forcing this thing into the standard would be
> useful. Probably alerting the ADQL users might be enough.
>
> Cheers,
>      Marco
>
>
>>
>>>>> Marco Molinaro <molinaro at oats.inaf.it> 07/05/16 3:32 PM >>>
>>
>> Dear Mark, DAL,
>> I think this is an erratum, with x and y switched in the description.
>> Cheers,
>> Marco
>>
>> 2016-07-05 15:25 GMT+02:00 Mark Taylor <M.B.Taylor at bristol.ac.uk>:
>>> Dear DAL,
>>>
>>> table 1 of REC-ADQL-2.0 defines the MOD function thus:
>>>
>>> Name Arg type Return type Description
>>> --------- -------- ----------- -----------
>>> mod(x, y) double double Returns the remainder of y/x.
>>>
>>> but as far as I can see, SQL 2003 (I presume 92 as well) and all
>>> the TAP services that I generally use define the arguments the other
>>> way around, i.e. returning the remainder of x/y.
>>>
>>> Am I misreading something or is this an erratum candidate?
>>>
>>> Mark
>>>
>>> --
>>> Mark Taylor Astronomical Programmer Physics, Bristol University, UK
>>> m.b.taylor at bris.ac.uk +44-117-9288776 http://www.star.bris.ac.uk/~mbt/
>>



-- 
Patrick Dowler
Canadian Astronomy Data Centre
Victoria, BC, Canada