On Dec 20, 2007, at 8:50 AM, Ivan Sergio Borgonovo wrote:
On Wed, 19 Dec 2007 17:24:52 +0100
Ivan Sergio Borgonovo <mail@xxxxxxxxxxxxxxx> wrote:
I've something like this:
create table i (
iid serial primary key,
name varchar(32)
);
create table p (
pid serial primary key,
iid int references i(iid) on delete cascade,
name varchar(32)
);
create table c (
bid serial primary key,
pid int references p(pid) on delete set null
);
insert into i values(default,'i');
-- default proprieties (singularity)
insert into p values(-1,null,'default p');
insert into p values(default,1,'this p');
insert into p values(default,1,'that p');
insert into c values(default,null);
insert into c values(default,1);
insert into c values(default,-1);
let's say I'd like to associate c with a name (the propriety)
a null c.pid means I still have to assign a propriety or the
previously assigned propriety is not anymore available.
I'd like to have a way to say take the propriety from i and the
above is what I came out with.
But that introduces a singularity.
Any better design? I don't like to write a schema that needs data
inside to have a meaning.
If not how can I protect the singularity from accidental delete?
Most of the db will be accessed through functions and this is a
step.
An alternative design could be
create table c (
bid serial primary key,
usedefault boolean,
pid int references p(pid) on delete set null
);
where
usedefault=true -> use default
usedefault=false -> use i.pid
usedefault is null -> not yet assigned
Ivan, after reading both of your posts I'm still not sure what you
mean or are trying to do. What do you mean by a singularity? By
propriety do you mean property? Can you give an example with more
descriptive names than i, p, and c?
Erik Jones
Software Developer | Emma®
erik@xxxxxxxxxx
800.595.4401 or 615.292.5888
615.292.0777 (fax)
Emma helps organizations everywhere communicate & market in style.
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