On 29.07.24 17:17, Tom Lane wrote:
I wrote:
I think the page is technically correct, but I'm inclined to duplicate
this text from the CREATE DOMAIN page:
where domain_constraint is:
[ CONSTRAINT constraint_name ]
{ NOT NULL | NULL | CHECK (expression) }
rather than making readers go look that up.
Actually, there *is* a bug in the description, because experimentation
shows that CREATE DOMAIN accepts NULL in this syntax (as advertised)
but ALTER DOMAIN does not. We could alternatively decide that that's
a code bug and make ALTER DOMAIN take it, but I don't think it's worth
any effort (and this behavior may actually have been intentional, too).
I think we should just add
where domain_constraint is:
[ CONSTRAINT constraint_name ]
{ NOT NULL | CHECK (expression) }
to the ALTER DOMAIN page, and then remove the claim that it's
identical to CREATE DOMAIN.
There was some discussion about these issues (ALTER DOMAIN vs CREATE
DOMAIN reference page, as well as the NOT NULL constraint syntax) in and
around
<https://www.postgresql.org/message-id/a4a344ea-9e79-4c42-a9af-899f85bd7...@eisentraut.org>.
All that ended up dying because the NOT NULL constraints feature was
reverted. But there were some subtle details about why the syntax is
the way it is and/or whether that's really intentional and how to
document it. Might be worth reviewing again.
