Hi,
I recently stumbled upon a really cool feature in DB2: distinct types.
DB2 lets you define your own types (just as Postgres) but with the added benefit that you
can mark them such that they are _not_ comparable, e.g. to avoid comparing "apples
to oranges".
Take the following example:
create type sno as varchar(50)
with comparisons;
create type pno as varchar(50)
with comparisons;
create table s
(
sno sno not null primary key,
.... other columns
);
create table p
(
pno pno not null primary key,
.... other columns
);
The following query will be rejected because sno and pno are not comparable
(even though both are varchar columns):
select *
from p
join s on s.sno = p.pno;
I wonder if a similar behaviour can be achieved with Postgres' types as well.
As a type definition in Postgres can also include comparison functions, I have
the feeling that this should be possible, but I don't have an idea on how to
start to be honest.
Any ideas?
Regards
Thomas
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