Re: Design problemi : using the same primary keys for inherited

David Pradier wrote:
> Well yes, i find your system very interesting and will maybe use it as
> solution for another problem we have ( :-) ), but i fail to see where
> it makes use of a primary key referencing another primary key ?

As regards the issue of one primary-key referencing another, I can't see
any problem. You want 0 or 1 references from table B to any row in table
A - this does that without any fuss or complication.

A primary key is a value (or set of values) like any other. It is unique
over any one table, but nothing says it can't be the same as a value in
some other table.

The other way would be something like:

CREATE TABLE A (
id serial not null unique,
aval text,
primary key (id)
);
CREATE TABLE B (
id serial not null unique,
aref int4 not null unique references A,
bval text,
primary key (id)
);

So - in table B we now have two candidate keys (id, aref) and above I've
chosen "id" as the primary-key. But I can eliminate "id" completely and
not lose any of the meaning of table "B" - which tells me that I was
wrong to think the rest of the table was dependent on "id". So, I must
have been wrong in making "id" a primary-key and since it has no meaning
of its own, I can eliminate it.

CREATE TABLE B (
aref int4 not null unique references A,
bval text,
primary key (aref)
);

--
Richard Huxton
Archonet Ltd