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.
