Re: composite Unique constraint and null

Interestingly enough, even though one "null" does not equal another "null", i.e. any comparison with NULL is always false, a unique index on (col1, col2) throws a unqiue constraint violation when you insert a second (1,null). It appears that for the index (1,null) IS equal to (1,null) - or does the unique index use reverse logic and checks if (1,null) <> (1,null) and, since this is false, concludes that (1,null) must be equal (1,null) and therefore violate the constraint ;-)

Jared Still wrote:

> A unique constraint can be used for this.
>
> Have you tried it?
>
> --
> Jared Still
> Certifiable Oracle DBA and Part Time Perl Evangelist

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Regards

Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com
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