On Mon, 2010-10-25 at 14:11 -0400, Robert Haas wrote:
> On Mon, Oct 25, 2010 at 2:01 PM, Jeff Davis <pgsql@j-davis.com> wrote:
> > On Mon, 2010-10-25 at 12:20 -0500, Kevin Grittner wrote:
> >> It would be very useful to be able to specify a granularity -- for
> >> example timestamps with a five minute granularity would be useful
> >> for scheduling appointments. In some cases the granularity might be
> >> inferred -- if we have a domain defined as numeric(13,2), it would
> >> be nice if the default granularity was 0.01::numeric.
> >
> > I don't think typmod really helps us much. It's more a property of the
> > column than the type.
> >
> > To specify different granularities, I don't think we can avoid
> > specifying new types with their own entries in pg_type.
>
> Why?
Because typmod doesn't survive through a function call. Even if it did,
I don't think typmod has a real answer for type promotion, implicit
casting etc.
If we lose the typmod (and therefore the granularity), then a function
like "adjacent" is difficult to answer if we use a closed-closed
canonical representation (as you suggested); and if we use a closed-open
representation then it's difficult to answer a question like whether a
range contains a specific timestamp.
Can I turn the question around and ask how you intend to make it work
without new entries in pg_type?
Regards,Jeff Davis