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

David Pradier wrote:
>>Most of the inheritance i've seen done in databases retain the parent primary as a foreign key and a primary key.
Thatbeing said, only you and your team can decide if more than one object will extend a base class. If you were doing
somethingmore like this
 
>>person -> sweepstakes entry
>>to model a sweepsakes entry is a person, and you allow a person to enter a sweepstakes more than once, but to enter a
contestthe user must provide a unique email address, then you could not just use a foreign key as the primary key in
sweepstakes,since the primary key would disallow multiple entries in sweepstakes entry, you would then use a serial
datatype in both person and sweepstakes along with the foriegn key in sweepstakes from person.
 
>>The answer depends on the need. Hope that helps.
> 
> 
> Thanks Russ, but well...
> It doesn't help me a lot. Our needs seem to allow that we use an id as
> primary key and foreign key at the same time.
> What i fear more is that it be against a good database design practice,
> because leading to potential problems.
> 
> I give a clearer example :
> 
> CREATE TABLE actor (
> id_actor serial PRIMARY KEY,
> arg1 type1,
> arg2 type2
> )
> 
> CREATE TABLE person (
> id_person INTEGER PRIMARY KEY REFERENCES actor,
> arg3 type3,
> arg4 type4
> )
> 
> Don't you think it is a BAD design ?
> If it isn't, well, it will expand my database practices.
> 

It *is* a bad design.  You should not do this.  After all, how is that 
any different than this?

CREATE TABLE actor_person ( id_actor serial PRIMARY KEY, arg1 type1, arg2 type2 arg3 type3, arg4 type4 )

Furthermore, inheritance is almost certainly the wrong relationship type 
here.  Normally, Actor would be a Role that a Person would be playing:

create table role(  id serial primary key,    -- 1  name char(20) not null    -- "Actor"
);

create table person(  id      serial primary key,        -- 1  name    char(20) not null,        -- "David"  role_id
intnot null references role    -- 1
 
);

> David

> 

-- 
Daryl Richter
Director of Technology

((         Brandywine Asset Management          ) ( "Expanding the Science of Global Investing"  ) (
http://www.brandywine.com          ))