Re: when to use NULL and when to NOT NULL DEFAULT ''

Peter Eisentraut wrote:
> Am Freitag, 8. Oktober 2004 07:22 schrieb Miles Keaton:
>
>>What's the prevailing wisdom & best-practice advice about when to let
>>a varchar (or any) column be NULL, and when to make it NOT NULL
>>DEFAULT '' (or '0000-00-00' or whatever) - in PostgreSQL?
>
> Briefly, you always do the first and never do the second.

Speaking of NULLs, what does the relational model ideal suggest for
missing information?

a) no NULL at all;
b) NULL and N/A;

I've read both, a) in "handling missing information without NULLs"
articles and b) in Joe Celko's book ("Codd proposed two kind of missing
information: NULL for unknown and N/A for not applicable").

--
dave