Antonios,
> Pascal says: use NULL only for missing, not for inapplicable. Here the
> state is inapplicable unless the country is US.
>
> What should I do instead? Create another table, "gstates"?
>
> id (PK and FK to gaddresses)
> state (FK)
>
> Is this overkill?
Yes. I'd say that null is an example of "acceptable denormalization".
Alternately, instead of using NULLs, I would suggest using a zero-length
string or "XX" to indicate non-applicability -- this would give you a clearer
indication, and allow you to avoid messy CASE WHEN IS NULL and COALESCE
queires. The zero-length string is particularly attractive as it lends
itself to easy concatination of addresses.
Regardless of which approach you take, you want to make sure that it is *only*
used for non-US addresses. So you will want to add a table constraint
enforcing the state code for US addresses.
Also, IME, many foriegn addresses have a region or province attached to them.
For databases including international addresses, I frequently have a generic
"province" field which covers both US states and foriegn regions, and enforce
consistency by using a reference list which includes both countries and
provinces/states.
--
-Josh Berkus
Aglio Database Solutions
San Francisco