Re: Question about One to Many relationships

They haven't responded me as of yet. There should be a band associated
with each album -- this is handled in code, but other than that this
is the only relational db way I can think of to do it.

Thanks!
Todd

On 3/24/06, D'Arcy J.M. Cain <darcy@druid.net> wrote:
> On Fri, 24 Mar 2006 11:52:31 -0500
> "Todd Kennedy" <todd.kennedy@gmail.com> wrote:
> > So I've got two tables, one for albums and one for bands, for
> > simplicity's sake, they look like this:
> >
> > CREATE TABLE bands (
> > id serial PRIMARY KEY,
> > name varchar(64) NOT NULL CHECK( name <> ''),
> > UNIQUE(name)
> > );
> >
> > CREATE TABLE albums (
> > id serial PRIMARY KEY,
> > name varchar(128) NOT NULL CHECK( name <> '')
> > );
> >
> > And I want to link the band to the album, but, if the album is a
> > compilation it'll be linked to multiple band.ids, so i can't just add
> > a column like:
> >
> > band_id integer REFERENCES band (id)
> >
> > to the albums table, othewise i'd have to duplicate the albums in the
> > table (one record for each band associated with an album).
> >
> > I thought a lookup table would be appropriate here, so like:
> >
> > CREATE TABLE bands_on_album (
> > id serial PRIMARY KEY,
> > band_id integer REFERENCES band (id),
> > album_id integer REFERENCES albums (id)
> > )
> >
> > but i'm being told this is "wrong"
>
> Wrong in what sense?  I can see issues depending on what your
> requirements are.  Well, one issue.  There is nothing in the above
> definition that guarantees that every album has at least one band on
> it.  Is that an issue in this system?  Otherwise, I can't see anything
> wrong from a relational database POV.
>
> What are people saying is wrong about it?
>
> --
> D'Arcy J.M. Cain <darcy@druid.net>         |  Democracy is three wolves
> http://www.druid.net/darcy/                |  and a sheep voting on
> +1 416 425 1212     (DoD#0082)    (eNTP)   |  what's for dinner.
>