On 10/23/23 18:53, Tom Lane wrote:
1. Domains are data types, with the proviso that NULL is always a valid value no matter what the domain constraints might say. Implementation-wise, this'd just require that CoerceToDomain immediately return any null input without checking the constraints. This has two big attractions:
(1A) It satisfies the plain language of the SQL spec about how CAST to a domain type behaves.
I agree with all of your proposal, except for this part. I think the shortcut in the General Rules of <cast specification> is an oversight and I plan on submitting a paper to fix it. The intention is, in my view, clearly to check the constraints upon casting. What other explanation is there since the result type is still the domain's base type[*]?
[*] In the standard, not in our superior implementation of it. -- Vik Fearing
