Re: Limits

From: JOG <jog_at_cs.nott.ac.uk>
Date: Fri, 25 Jul 2008 14:58:38 -0700 (PDT)
Message-ID: <7a205ced-bd9c-47b9-8320-63200e13fed7@f63g2000hsf.googlegroups.com>


On Jul 25, 7:04 pm, Tegiri Nenashi <TegiriNena..._at_gmail.com> wrote:
> On Jul 25, 7:30 am, JOG <j..._at_cs.nott.ac.uk> wrote:
>
> > As it is with ORDER BY I guess, which is supposed to spit out a linear
> > ordering where only a partial ordering may exist.
>
> Could you please be more specific? All SQL datatypes I know (well,
> those that I'm using -- string, number, date) are total orders. What
> partial ordered datatype do you have in mind?

the tuple itself. For instance if we have relation: R := {w, x, y}

where the tuples are:

w := (a:1, b:1)
x := (a:2, b:2)
y := (a:3, b:2)

then "ordering by a" yields a total ordering over R: {(w, x), (w,y), (x,y)}

but "ordering by b" gives the partial ordering: {(w, x), (w,y)}

Regards, J. Received on Fri Jul 25 2008 - 16:58:38 CDT

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