Re: Relational database design book

rshepard(at)appl-ecosys(dot)com (Rich Shepard) writes:
>
> [2] Strangely enough -- to me, at least -- the lack of full support for
> date- and time-based SQL in database tools such as PostgreSQL is puzzling.
> Virtually all business-related databases (think accounting systems as a
> prime example) depend on dates. So do many scientific databases.

The support for temporality in PostgreSQL seems above average as far
as I can see...

PostgreSQL has pretty nice time types between the timestamptz type and
interval.

What strikes me as being missing is the ability to create
temporally-aware foreign keys.

That is, suppose the schema is:

create table1 (
nearly_pk integer not null,
from_date timestamptz not null default now(),
to_date timestamptz not null default 'Infinity',
constraint dating_t1 check (from_date < to_date)
-- probably some other data...
);

I'd like to be able to do two more things:

a) Treat the date range as part of the primary key (which isn't
forcibly hard),

b) Have references to table1 that point to the time range for the
"nearly_pk" value but which are a little more liberal with the dates.

create table2 (
t2pk integer primary key,
nearly_pk integer not null,
from_date timestamptz not null default now(),
to_date timestamptz not null default 'Infinity',
-- And have a "foreign key" that requires that
-- for tuple in table2 the combination (nearly_pk, from_date, to_date)
-- is *contained* by relevant ranges of (nearly_pk, from_date, to_date)
-- on table1
foreign key (nearly_pk) references
table1(nearly_pk) with temporal (table2.from_date, table2.to_date)
contained_by (table1.from_date, table1.to_date)
);

I don't think the syntax there is necessarily quite right; I'm just
hoping to express the idea successfully.

I could presumably do this with a trigger; have been trying to avoid
that thus far.

There are, of course, other ways of treating temporality; that is part
of why it's early to treat this approach as worth putting into syntax.
--
output = ("cbbrowne" "@" "acm.org")
http://cbbrowne.com/info/finances.html
"When the grammar checker identifies an error, it suggests a
correction and can even makes some changes for you."
-- Microsoft Word for Windows 2.0 User's Guide, p.35: