[quote user="bstorer"]Look, I know the mathematics behind the relational model, and I'm certain Welbog does, too.[/quote]I remember when I took database design in university and we covered tri-state logic. I thought, "Hmm, that's neat, I guess," when it was first introduced...

[quote user="niik"] Why this is not obvious? Simple, because people mix null with the empty - those two terms are not synonyms. The statement "Pear is not a member of set containing apple and empty box" is true. But, statement "Pear is not a member of set containing apple and...

[quote user="LoztInSpace"]Of you want yes/no then use NOT NULL constraints. If you allow nulls in boolean then you need to deal with tri-state. How can you not? You have 3 values! As for the control structures, they are there - you just don't like them (assuming you mean using IS NULL)...