Re: check constraint

On Mon, Jun 02, 2003 at 10:52:00 +0200,
  erwan ancel <erwan.ancel@free.fr> wrote:
> Hi,
> I would like to know if it is possible to set "complex" constraints on
> databases such as:
>
> A->B means that in table A, each record references a record of table B
> (or NULL)
>
> so we have:
>
> A->B
> C->B
> D->C
> D->A
> constraint: for one record of D, D->A->B = D->C->B
>
>     Hope it is clear enough.

It looks like you are talking about foreign keys. Postgres has foreign key
constraints. You can look at the create table documentation to see how
to define them when creating a table.