Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?
Date: Thu, 13 Feb 2003 14:01:11 -0800
Message-ID: <3GU2a.12$O%2.121_at_news.oracle.com>
"Lauri Pietarinen" <lauri.pietarinen_at_atbusiness.com> wrote in message
news:3E4B8137.2080204_at_atbusiness.com...
> 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.
I wonder why A INTESECT B row multiplicities are not multiplied in the Bag's INTESECT definition. Well,
{<Smith, 20>, <Smith, 20>} INTERSECT {<Smith, 20>,<Smith, 20>, <Smith, 20>}
=
= {<Smith, 20>,<Smith, 20>, <Smith, 20>,<Smith, 20>,<Smith, 20>, <Smith,
20>}
might seem counterintutive, but we don't have to appeal to layman's common sence, right? Just make the definition that is consistent with algebraic rules, and adjust "common sence" to it. Or, am I missing some pitfall? Received on Thu Feb 13 2003 - 23:01:11 CET