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Date: Wed, 26 Oct 2005 17:22:12 -0700
From: Rick Hillegas <Richard.Hillegas@Sun.COM>
Subject: Re: Unique constraints on multiple fields with one nullable
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Hi Dan,

I believe that the Sybase behavior is correct. I have logged bug 653 to 
track this issue.

Regards,
-Rick

Dan Meany wrote:

>I noticed that in Derby a unique constraint on two
>columns A and B, with B nullable, will prevent
>inserting two identical records that contain NULL in
>B.
>
>This is different from some other databases such as
>Sybase that do allow it (I assume where the null
>records are not in stored as part of the unique
>index).
>
>I noticed this while transfering data from Sybase to
>Derby using Apache dbutils and getting rejected
>duplicate records.
>
>  
>