Re: How to enforce uniqueness when NULL values are present?

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On 03/10/07 18:22, Christian Schröder wrote:
> Peter Eisentraut wrote:
[snip]
> I know that it's always dangerous to quote the Wikipedia. Let me do it
> anyway: "Attributes in tables in SQL database management systems can
> optionally be designated as NULL. This indicates that the actual value
> of the column is unknown _or not applicable_."
> (http://en.wikipedia.org/wiki/Null_%28SQL%29) This is exactly what I
> once learned about NULL values, and "not applicable" is exactly why I
> use NULL values in my example.

I've never heard of NULL meaning "not applicable", but only
"unknown". To me, "not applicable" screams "denormalized".

So, I'd put 1900-01-01 (or whatever is your application's epoch) in
those date fields with NULL values, because that's their effective date.

>
> Regards,
> Christian
>

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