ADQL Erratum 2

[Walter Landry]

Grégory Mantelet <gmantele at ari.uni-heidelberg.de> wrote:
>> (2) Wouldn't it be preferable if we said, in the erratum, as the new
>> text:
>>
>>    rand([x]) -- Returns a random value between 0.0 and 1.0.  The
>>    argument was initially intended to provide a random seed, if given.
>>    It turned out, however, that in concept and implementation, it is
>>    hard to attach stable semantics to this notion.  Hence, while an
>>    argument is accepted for backward compatibility, clients should
>>    expect that the 1-argument function behaves exactly like the
>>    0-argument one.
>>
>> Or something like this?
> 
> 
> I completely agree to make the seed parameter optional.
> 
> But since this seed parameter is optionally accepted by some DBMS used
> on some existing TAP implementation, I am not entirely convinced that
> we should disable the possibility to use a seed parameter. Then, I
> don't have a strong opinion about the random generation and the need
> of "regenerating" the random numbers with a seed in a database usage.

My take is that if it is not implementable for all backends, it should
not be in the standard.  Silently changing rand(x) into rand() is just
adding a boobytrap for users.  So I would not even make it optional.
If you want to offer it to your users, that would be an extension.

Cheers,
Walter Landry