On Sun, Aug 29, 2004 at 15:38:45 -0600,
Scott Marlowe <smarlowe@qwest.net> wrote:
> On Sun, 2004-08-29 at 15:30, Bruno Wolff III wrote:
> > On Fri, Aug 27, 2004 at 13:32:07 +0530,
> > Yateen Joshi <yjoshi@starentnetworks.com> wrote:
> > > Hi,
> > >
> > > I have got a table which is supposed to contain only one row. It does
> > > not have any primary keys defined.
> > > So, essentially, when a new insert happens in that table, I would like
> > > it (the insert) to fail if there is already a row existing in that
> > > table.
> > > How can I do that? Can I add any constraints? Or do I need to write a
> > > separate trigger for the same?
> >
> > A simple way to force this is to add a primary key and a constraint
> > that forces the primary key to be a particular value.
>
> Is it reasonable / possible to add a check constraint something like
> select count(*) from table <=1?
It should be possible to do that with an after trigger, but it is a bit
more work to set up. As long as the table gets vacuumed, either way
is probably reasonably fast.