Databasen - NULL dates

[ti@lemonia.org]

Dave Cross wrote:
> NULL is the unknown value. Your dates are unknown. Sounds like a
> perfect match to me. I'd be interested in hearing the other point of
> view.

Well, Chris Date ("Database in Depth", etc) seems to think they're evil,
mainly because of unpredictable or weird behaviour of ternary logic. As
far as I could see, Date doesn't address resulting issues like:

* You then spawn a large number of one-to-many tables to hold optional values
* Minor amendments to enterprise rules (ie. varying which fields are
optional)
  would then result in a denormalised schema
* Queries still need to give the right answer, whether or not any of the
  optional values exist or not. This is quite possibly just as tricky as
  auditing queries for correct ternary logic in NULL cases.

I also note that Mr Cross rated Mr Date's book rather highly, despite
disagreeing with what appears to be something of a bugbear for Mr Date...

Tim