Re: (redefinition) alter table, add foreign key constraint

On Tue, 17 Oct 2000, Matthew Kennedy wrote:

> bmccoy@chapelperilous.net wrote:
> > On Tue, 17 Oct 2000, Matthew Kennedy wrote:
> > > Is it possible to perform an alter table with add foreign key constraint
> > > in PostgreSQL? We are trying to support multiple DBMS in our project by
> > > keeping to a common, compatible denominator. Oracle, supports such a
> > > construct. Does (or might) PostgreSQL support this feature?
> > Yes...
> > ALTER TABLE <table> ADD <constraint definition>
> > Brett W. McCoy
>
> Firstly...
>
> A little redefinition of my question is in order. If I try doing this:
>
> create table things (name varchar(20), state(2));
> create table states (abbreviation varchar(2));
> alter table things
>     add foreign key (state)
>     references states (abbreviation);
>
> Postgres responds with:
>
> NOTICE:  ALTER TABLE ... ADD CONSTRAINT will create implicit trigger(s)
> for
> FOREIGN KEY check(s)
> CREATE
>
> I am wondering what the implications of postgres using implicit triggers
> for foreign key constraints are? I guess if there were no implications
> (ie. implicit triggers were a perfect implimentation of foreign keyt
> constraints), then there would be no warning message?

Actually, it's just to let you know.  Similar to the creating unique index
messages that are(were) in for unique/primary key.

> Secondly...
>
> Postgres doesn't seem to take the name of a foreign key (it's a parse
> error to include it). This is slightly different to what SQL92 and
> Oracle allow. I beleive I should have been able to write:
>
> alter table things
>     add foreign key things2states (state)
>     references states (abbreviation);

I'm pretty sure the correct SQL92 syntax is:
alter table things
 add constraint things2states foreign key (state)
 references states (abbreviation);