Re: fk problems with 0..n relations

On Mon, Dec 05, 2005 at 01:45:37 -0000,
Luis Silva <lfs12(at)hotmail(dot)com> wrote:
> I there, i'm having a problem. i have a table(1) that is connected with two multiple table (2 and 3). the problem is that the table 1 might have one of the tables (2 or 3, or both). how can i make this relationship in sql. Resuming, table 1 as a 0..n relation with table 2 and 3. thanks in advance.

Normally you just have tables 2 and 3 refer to table 1 and not the other way
around.

If you need to make sure that the entry in table 1 corresponds to at least
one entry in table 2 or table 3, then you can have table 1 refer to both
table 2 and table 3, but allow nulls. Then you use a constraint to make
sure at least one of the references is not null.