Re: Foreign key question

Mensaje citado por Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Terry Lee Tucker <terry(at)esc1(dot)com> writes:
> > From the HTML docs:
> > "The referenced columns must be the columns of a unique or primary key
> > constraint in the referenced table."
>
> > I personally don't know of a work around. Maybe some of the others do.
>
> There is no workaround, because foreign keys don't make any sense if
> there isn't a uniquely identifiable referenced row.

A better way to understand it is:

Foreign keys are many to one assignments.

Try to think of it as a function (mathematicaly speeking): You can't have an element
from the domain end up on two different elementos of the co-domain.

In simbols:

If f(x) = y and f(x) = z => y = z

Those this bring insight?

P.D.: Aparently you are having problems with your database model.

--
select 'mmarques' || '@' || 'unl.edu.ar' AS email;
---------------------------------------------------------
Martín Marqués | Programador, DBA
Centro de Telemática | Administrador
Universidad Nacional
del Litoral
---------------------------------------------------------