From: Martijn Tonies
Date: February 23 2005 2:51pm
Subject: Re: UNIQUE Key Allowing Duplicate NULL Values
List-Archive: http://lists.mysql.com/mysql/180445
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> 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.

I can easily continue arguing about this ... :-)

NULL is not a value. There's no such thing as a "null value". NULL
is a state. NOT NULL is a state. That's the two possible states
of a column.

Why do you allow NULL, in this case? And what does it mean?

With regards,

Martijn Tonies
Database Workbench - developer tool for InterBase, Firebird, MySQL & MS SQL
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