On Fri, May 3, 2024 at 2:47 PM Laurenz Albe <laurenz.albe@cybertec.at> wrote: > > On Thu, 2024-05-02 at 08:23 -0700, David G. Johnston wrote: > > Version 2 attached. Still a draft, focused on topic picking and overall structure. > > I'm fine with most of the material (ignoring ellipses and typos), except this: > > + The NOT NULL column constraint is largely syntax sugar for the corresponding > + column IS NOT NULL check constraint, though there are metadata differences > + described in create table. >
the system does not translate (check constraint column IS NOT NULL) to NOT NULL constraint, at least in domain.
I'll change this but I was focusing on the fact you get identical user-visible behavior with not null and a check(col is not null). Chain of thought being we discuss the is not null operator (indirectly) already and so not null, which is syntax as opposed to an operation/expression, can leverage that explanation as opposed to getting its own special case. I'll consider this some more and maybe mention the catalog dynamics a bit as well, or at least point to them.
drop domain connotnull cascade; create domain connotnull integer; alter domain connotnull add check (value is not null); \dD
This reminds me, I forgot to add commentary regarding defining a not null constraint on a domain but the domain type surviving a left join but having a null value.