Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?
Date: 11 Mar 2003 22:23:11 +0100
Bob Badour wrote:
>"Jan Hidders" <jan.hidders_at_REMOVE.THIS.ua.ac.be> wrote in message
>> Bob Badour wrote:
>> >"Jan Hidders" <jan.hidders_at_REMOVE.THIS.ua.ac.be> wrote in message
>> >> I'm not convinced that bags are never needed. [...] 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.
>> >Such as?
>> Such as combining two iterations over the same bag into one. It's pretty
>> easy to see that
>> SELECT f(x)
>> FROM x IN
>> SELECT g(y)
>> FROM y IN Y
>> is the same as
>> SELECT f(g(y))
>> FROM y in Y
>If we don't have bags, it is not an issue. Is it?
- Jan Hidders