Do you mean that NULL <> NULL and NULL infects boolean logic?
NULL is always an awkward thing to deal with - how you want to handle it depends on the specific thing you're trying to accomplish. I'd probably prefer it if NULL equaled NULL when dealing with where conditions but it actually makes join evaluations a lot cleaner - if NULL equaled NULL then joining on columns with nulls would get really weird.
At the end of the day IS NULL and IS DISTINCT FROM/IS NOT DISTINCT FROM exist so you can handle cases where it'd be weird.
I think that's just a question on syntactic sugaring here - so, concretely, what would that mean for comparison operators? If I wanted to `id = id` and both were nullable would I need to express that as two layers of statements where I tried to unwrap both sides first or would we have a maybe vs maybe comparison operator - if we had such an operator what would it do in this case?
You’d have to unwrap, usually with convenient mechanism for it —pattern matching
The problem is that id = id is fundamentally incorrect for a nullable column. You should have done id is not null and id = id. And you shouldn’t have been allowed to do the first anyways, because nothing good can come of it (there is no sane semantics to stuffing a trinary logic into a boolean algebra, and SQL chooses one of the many insane options, leading to both false positive and false negative matches depending.) the only correct answer is not to do that.
I can understand how that would make things more explicit - but given how common nullability is in the realm of databases I think it'd be a bad idea to force that much syntax in a situation where id=id is essentially what we want to discuss - especially since columns becoming potentially null is so trivial to achieve (even when impossible due to model constraints) as soon as you start throwing left joins in the mix.
Sometimes you really want explicit, rather than dealing with the errors caused by implicitness. And with a language that has proper support for things like Maybe, there isn't that much syntax.
It's true that you have to adopt a completely different language, but when that language saves you from potentially expensive bugs, it becomes appealing.
I think it handles all the 3VL problems I've encountered in SQL, but that doesn't mean it handles all possible 3VL problems. It also might not make any sense to anyone except me.
It's been a while since relational algebra so I don't feel confident saying "Yes" or "No" (I guess you could say my reply is Null) - but that seems like a really good base approach - especially having a state for being uncertain whether something is nullable or not... having an operator embeded fallback approach also seems to be a lot more usable for the developer.
Also, this is an aside, but is your thing named after Snake Plissken?
Yeah, kind of. I have seen Escape From New York but I don't really remember it. I was more aware of the character via the reference/homage in Metal Gear Solid 2. In any case, I don't love the name but the obvious choice (Racquel) was already taken and "Plisqin" had zero Google results so I said "meh, good enough."
NULL is always an awkward thing to deal with - how you want to handle it depends on the specific thing you're trying to accomplish. I'd probably prefer it if NULL equaled NULL when dealing with where conditions but it actually makes join evaluations a lot cleaner - if NULL equaled NULL then joining on columns with nulls would get really weird.
At the end of the day IS NULL and IS DISTINCT FROM/IS NOT DISTINCT FROM exist so you can handle cases where it'd be weird.