Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?
Date: Thu, 13 Feb 2003 19:36:49 +0200
>>and better optimisations would be obtained without duplicates"
>No. In fact, in theory, all optimizations that can be done in a set-based
>algebra can also be done in a bag-based algebra but not the other way
So you in fact disagree with Date on that one?
Is not optimisation (at least partly) a question of query transformations? I understand that more transformations are available when we operate with sets that if we operate with bags. Even the excerpt from the book seems to suggest this:
For instance, you may have learned set-theoretic laws such as A INTERSECT (B UNION C) = (A INTERSECT B) UNION (A INTERSECT C), which is formally the "distributive law of intersection over union." This law holds for sets, but not for bags.
Lauri Pietarinen Received on Thu Feb 13 2003 - 18:36:49 CET