Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?

Lauri Pietarinen wrote:
>Jan Hidders wrote:
>>Lauri Pietarinen wrote:
>>>
>>>I was not really trying to impress you by those references. I was just
>>>figuring that since we were talking about aggregates we should have some
>>>reference (if not agreement) as to what an aggregate function means.
>>
>>Why do you think there is disagreement about that?
>>
>Well, from reading those articles by Date I don't get the impression that
>bags provide more optimisations than sets regarding aggregates as you
>suggested.

The "that" in my sentence referred to your "what an aggregate function means". I'm curious why you think that the meaning of the term is controversial.

>>>Regarding point 5) I challenge you to give me just
>>>*one* *real* *world* *example* in which duplicates
>>>would actually be of use to the end user.
>>
>>I never said there was, and even if there was you could simulate this in a
>>set-only model.
>>
>>So, what is your point exactly?
>>
>If nobody needs them (bags) why support them? Even if the cost is zero?

I'm not convinced that bags are never needed. There's a reason that mathematicians introduced it; they needed it to model certain things. What about Petri nets, for example? And if you are then going to simulate them with sets then the cost might become negative because the set-based optimizer might miss certain optimizations that would have been easier to spot for a bag-based optimizer.

• Jan Hidders