Re: 3 value logic. Why is SQL so special?

Gene Wirchenko schrieb:

> Volker Hetzer <firstname.lastname_at_ieee.org> wrote:
> 
> [snip]

>> What I don't understand is that everyone who decries nulls, somewhere
>> works with default values. Ok, big deal, NULL is an universally applicable
>> default value that cannot be confused with real data.
>> What am I missing?
>
> That it can be confused with real data. How?
Every interface worth its name has either a special flag or allows the mapping to a certain value upon reading it out of the database. And if not, then, at least in oracle, I can create a simple boolean (C convention) flag in the select list: select expr, nvl2(expr,0,1) Expr_Is_Null ...

> For one thing, NULL is
> *NOT* a value. It is the absence of a value. Conceptually, so is any other default value. Only, with NULL, the database agrees. With other default values I have to code it all in the sql.

Lots of Greetings!
Volker

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