From: "Paul DuBois" <[EMAIL PROTECTED]> To: "Jude Insley" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Subject: Re: Bug in UNIQUE?
> >The SQL below illustrates what I believe is a bug in MySQL up to and > >including 3.23.47. Essentially I need a unique key where one or more of > >the component fields of the unique key can be NULL. What seems to happen > >is that you can add "duplicate" rows if the value is NULL. > > This is how UNIQUE indexes work in MySQL. All values except NULL > must be unique. If you use a PRIMARY KEY instead, this won't happen. > Of course, the reason it won't happen is that PRIMARY KEY disallows > NULL entirely. I thought that UNIQUE indexes constituted what is known in the relational model as a "candidate key" and, AFAIR, none of the members in a candidate key may contain NULL values. - Carsten --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
