From: | Erik Price <eprice(at)ptc(dot)com> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: PRIMARY KEYS |
Date: | 2003-05-22 12:03:34 |
Message-ID: | 3ECCBC96.3070405@ptc.com |
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Thread: | |
Lists: | pgsql-general |
Martijn van Oosterhout wrote:
> On Wed, May 21, 2003 at 12:02:01PM -0400, Vivek Khera wrote:
>
>>>>>>>"MvO" == Martijn van Oosterhout <kleptog(at)svana(dot)org> writes:
>>
>>MvO> Number or Drivers Licence number as primary key is forbidden. If
>>MvO> you're permitted to have the information you're allowed to store
>>MvO> it but you sure as hell can't index your filing cabinets on it or
>>MvO> make it a primary key.
>>
>>What exactly is the difference between
>>
>>UNIQUE INDEX on a NOT NULL column of driver license numbers with no
>>other primary key on that table
>>
>>and
>>
>>PRIMARY KEY on that same column?
>>
>>The only thing that changed was the name.
>
>
> There's no *technical* difference, but a very large semantic difference.
> Whatever you use as your primary will become prolific.
One technical difference is that if you declare a column as a FOREIGN
KEY referencing another table without specifying a column within that
table, then the PRIMARY KEY of that table will be used as the target of
the FOREIGN KEY.
I think.
Erik
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