That's not the only time it is weird. There's even a whole book by one of the pioneers of the relational DB model, Date's "Database Technology: Nulls Considered

That's not the only time it is weird. There's even a whole book by one of the pioneers of the relational DB model, Date's "Database Technology: Nulls Considered Harmful" [1], covering many of the ways it is weird. [1] https://www.amazon.com/Database-Technology-Nulls-Considered-Harmful/dp/1634624769 https://www.amazon.com/Database-Technology-Nulls-Considered-...