Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?
Date: Thu, 13 Feb 2003 16:54:15 -0800
Message-ID: <jcX2a.16$O%2.38_at_news.oracle.com>
"Bob Badour" <bbadour_at_golden.net> wrote in message
news:4uW2a.1409$0G3.168661119_at_mantis.golden.net...
> "Mikito Harakiri" <mikharakiri_at_ywho.com> wrote in message
> news:irT2a.10$O%2.40_at_news.oracle.com...
> > Not
> > for aggregates:
> >
> > PROJECTION*AGGREGATE != AGGREGATE*PROJECTION
> >
> > for example
> >
> > select distinct S from (
> > select distinct SUM(SAL) from emp
> > )
> >
> > is not the same as
> >
> > select distinct SUM(SAL) from (
> > select distinct SAL from emp
> > )
> >
> > where i'm using SQL with the "distinct" keyword merely as a surrogate
for
> > true relational syntax ("distinct" is redundant after aggregate
operation,
> > of course).
>
> Why should the sum of all salaries equal the sum of distinct salaries?
select S from (
select SUM(SAL) S from emp
is the same as
select SUM(SAL) from (
Once again, this means that PROJECTION and AGGREGATE commute in the bag model. Received on Fri Feb 14 2003 - 01:54:15 CET