Re: View Updates Problem Statement
Date: Mon, 8 Sep 2003 18:02:15 -0700
Message-ID: <RM97b.28$741.254_at_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 Tue Sep 09 2003 - 03:02:15 CEST