Re: Range types

Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> On Tue, 2009-12-15 at 11:49 -0800, David Fetter wrote:
>> FWIW, I think it would be a good idea to treat timestamps as
>> continuous in all cases.

> I disagree. There is a lot of value in treating timestamp ranges as
> discrete.

> One big reason is that the ranges can be translated between the
> different input/output forms, and there's a canonical form. As we know,
> a huge amount of the value in an RDBMS is unifying data from multiple
> applications with different conventions.

Actually, that is exactly one of the reasons why what you propose is
a *bad* idea. You want to institutionalize application dependence on
a non-portable implementation detail, namely the granularity of machine
representation of what's in principle a continuous value. That's one
of the fastest routes to non-unifiable data I can think of.

> So, let's say one application uses (] and another uses [). If you are
> mixing the data and returning it to the application, you want to be able
> to provide the result according to its convention. You can't do that
> with a continuous range.

The above is nonsense. [1,2) and [1,2] are simply different objects.
A design that assumes that it is always possible to replace one by
the other is broken so badly it's not even worth discussing.

The only reason you'd have applications that fail to handle both open
and closed intervals would be if someone were to create an
implementation that didn't support both from the outset. Which we
need not and should not do.

> And things get more interesting: if you mix (] and [), then range_union
> will produce () and range_intersect will produce []. So now you have all
> four conventions floating around the same database.

Which is why it's a good idea to support all four...

regards, tom lane