[jhgb]

> It doesn't just mean "unknown". It can also mean "no value".

Isn't the canonical representation of known-no-value an absence of a tuple? Like as opposed to saying "There exists an employee X who works in department NULL", you simply don't make any claim about employee X working in a department? After all, when enumerating the members of a set, you're also omitting the enumeration of non-members of a set, and the law of excluded middle applies.

[Tostino]

Nulls will reappear in your queries due to joins even if none exists in your data model.

[jhgb]

Ah yes, they're the curse of SQL. Still doesn't seem to be a reason to not squash them out as much as feasible within the constraints of SQL.