Re: Foreign key refer to unique constraint????
From: Carlos <miotromailcarlos_at_netscape.net>
Date: 21 Jan 2004 00:09:10 -0800
Message-ID: <1de5ebe7.0401210009.1339e6e8_at_posting.google.com>
Date: 21 Jan 2004 00:09:10 -0800
Message-ID: <1de5ebe7.0401210009.1339e6e8_at_posting.google.com>
> foreign key also refer to unique constraint.
> (GREAT...)
>
> 1.then table that containt unique constraint act as master table?????
Yes.
> 2.IS unique constraint will replace with primary key??
> 3.Is unique constraint gives all fuctionality as primary key constraint???
The only diference between PK and UK (besides built-in indexes) is that UK can contain NULLs, whereas PK cannot. A given table could contain many rows with a NULL in the UK column (this is, the 'uniqueness' affects only NOT NULL columns).
Regards.
Carlos. Received on Wed Jan 21 2004 - 09:09:10 CET