Ron St-Pierre <rstpierre@syscor.com> writes:
> I just want to constrain the ysnDefault field to only allow one TRUE
> value for any companyID/associationID pair, with no restrictions on the
> number of FALSES.
You could do that with a partial unique index. There is an example
at the bottom of
http://www.postgresql.org/docs/7.3/static/indexes-partial.html
regards, tom lane
