Re: View Updates Problem Statement

From: Mikito Harakiri <mikharakiri_at_ywho.com>
Date: Mon, 8 Sep 2003 18:02:15 -0700
Message-ID: <RM97b.28$741.254@news.oracle.com>

"Mikito Harakiri" <mikharakiri_at_ywho.com> wrote in message news:Yw97b.27$741.210_at_news.oracle.com...
> 3. Constraints are views that evaluate to constants. For example, if we
> define
>
> view V3
> select max(sal) from (
> select sal from emp
> union
> select 1000 from DEE
> )
>
> then constraint "each emp has salary no more than 1000" can algebraically
be
> written as
>
> V3*x = 1000
>
> where "V3*x" means view V3 applied to a set of base relations x, and
"1000"
> means an output relation that has one tuple with a single value 1000.

Small increment, sorry.

It is even better to write constraint equation as

view V3
select max(sal)/1000 from (

     select sal from emp
     union
     select 1000 from DEE

)

V3*x = DEE

or still even better

view V3
select 1000 from DEE
minus
select max(sal) from (

     select sal from emp
     union
     select 1000 from DEE

)

V3*x = DUM

(Equations that evaluate to 0 are math favorits:-) Received on Mon Sep 08 2003 - 20:02:15 CDT