Nathan Boley <npboley@gmail.com> writes:
>> This statement seems to me to demonstrate that you don't actually
>> understand the concept of open and closed ranges.
> IMHO the first question is whether, for integers, [1,2] UNION [3,5]
> should be equal to [1,5]. In math this is certainly true, and defining
> 'next' seems like a reasonable way to establish this in postgres.
Well, that's nice to have (not essential) for data types that actually
are discrete. It's not a sufficient argument for creating a definition
that is flat out broken for non-discrete datatypes.
It might be worth pointing out here that the concept of an open interval
was only invented in the first place for dealing with a continuum.
If you could assume the underlying set is discrete, every open interval
could be replaced with a closed one, using the next or prior value as
the bound instead. There would be no need for two kinds of interval.
If you are intending to support UNION on intervals, you are going to
need some more-general representation anyway. (I trust you don't think
we will accept a datatype for which [1,2] UNION [3,5] works but
[1,2] UNION [4,5] throws an error.) So whether the code can reduce the
result of a union to a single range or has to keep it as two ranges is
only an internal optimization issue anyhow, not something that should
drive an artificial (and infeasible) attempt to force every domain to be
discrete.
regards, tom lane