Re: [Help]How to translate from Algebra->SQL and viceverse?

there is an assumption that there is some direct correlation between relational algebra and SQL which is not the case. relational theory was defined in order to establish a well defined set of rules for representing data and their relationships. SQL came later as a tool to extract information from a relational database.

kind of like the difference between theories of programming language design and a specific compiler. in moving from theory to practice, tradeoffs are always made for various reasons, but without the theory the implementation would often not be possible.

einstein first had to show e=mcc before the bomb could be made. the theory was well understood long before the development team learned how to cause an implosion allowing the reaction to begin when designing the first bomb using the theory.

"Joe "Nuke Me Xemu" Foster" <joe_at_bftsi0.UUCP> wrote in message news:t0ks96armtmpa9_at_corp.supernews.com...
> "macefindu" <changth9_at_hotmail.com> wrote in message
 news:20001108.235408.338888228.818_at_jedi.200.41.96.2...
>
> > I was wondering why do we must learn Algebra if it cant handle all SQL's
> > operators(ie: group by ... having ...). Just take a look at the demos
> > *.sql that came with Oracle, most of them contain codes that easily
> > exceed 20 select in one query!
>
> I think the GROUP BY and HAVING clauses, like ORDER BY, were added for
> grubby real-world purposes like creating reports. I don't think ordering
> is supposed to matter in the relational model.
>
> > The only one reason that came out of my mind was "to exercise our brain
 muscles".
>
> Just wait until your prof tells you how SQL was supposed to be for
> end users! Do a search on "Reisner" within this page:
>
> <http://www.mcjones.org/System_R/SQL_Reunion_95/sqlr95-System.html>
>
> --
> Joe Foster <mailto:jfoster_at_ricochet.net> Got Thetans?
 <http://www.xenu.net/>
> WARNING: I cannot be held responsible for the above They're
 coming to
> because my cats have apparently learned to type. take me away,
 ha ha!
>
>
Received on Sun Nov 12 2000 - 01:17:33 CET