Re: UNIQUE Key Allowing Duplicate NULL Values

[Harald Fuchs]

In article <DA749670ABB17C4994D03B34889179D8228EEB@stripped>,
"Gustafson, Tim" <tjg@stripped> writes:

> Martijn,
> The problem is that I don't want more than one row in the table that has
> a null value in the column.  As you've pointed out in your e-mail,
> there's a difference between NULL and BLANK.  It's not that I don't want
> NULL values, it's that I don't want MORE THAN ONE.

You really should change your requirements.  Since NULL != NULL, every
DB enforcing a single NULL row by a unique index would not be SQL.
You seem to want "some special value" to occur only once, but NULL is
no value at all.  Can't you make 0 or "" (the empty string) that
"special value"?