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

Home -> Community -> Usenet -> comp.databases.theory -> Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?

From: Lauri Pietarinen <lauri.pietarinen_at_atbusiness.com>
Date: Thu, 13 Feb 2003 19:36:49 +0200
Message-ID: <3E4BD7B1.3030900@atbusiness.com>

>
>
>>and better optimisations would be obtained without duplicates"
>>
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>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
>around.
>

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:

<quote>
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.
<quote/>

regards,
Lauri Pietarinen Received on Thu Feb 13 2003 - 11:36:49 CST