David, all,

D> Just like someone else was stating, if we had been unable to set the fields to
D> NULL, we would've had to have had a separate field for each value we were
D> collecting to declare it's possible NULL state.

the usefulness of having a special value that indicates that a value
is missing is unquestioned. The usefulness of NULL and tri-state
boolean logic as the SQL standard prescribes it is more problematic to
defend. Relational algebra doesn't know what a NULL is. So relational
databases shouldn't have known as well.

Ciao
--
Nando Dessena
mailto:nandod@...