NYCPHP Meetup

[Peter Lehrer]

I see.
I think I confused a primary key using a combination of columns in a table
versus having 2 primary keys in a table, which obviously can't exits.
Thanks for your help.

Peter

----- Original Message -----
From: "David Mintz" <dmintz at panix.com>
To: "NYPHP Talk" <talk at nyphp.org>
Sent: Saturday, June 14, 2003 11:40 PM
Subject: Re: [nycphp-talk] primary keys


> On Sat, 14 Jun 2003, Peter Lehrer wrote:
>
> > Is it possible to have two primary keys in one table, such as primary
key 1
> > and primary key 2, or is that a contradiction in terms? Would second
primary
> > key have to be a "unique"?
>
> You can only have one primary key. If you're thinking about a unique index
> on multiple columns, yes you can do that, and indeed there are situations
> where you do. You might not need any primary key in that case.
>
> I'll give you an example. I have a table called 'interpreter' (of
> languages) and a table called 'language'. Some interpreters have multiple
> working languages; lots of languages are spoken by more than one
> interpreter. You resolve the many-to-many relationship with a third table
> called interpreter_language which looks something like this (English is
> asumed in this particular application, so I only one the 'foreign'
> language to store each interpreters' language pair). Note the unique key:
>
> CREATE TABLE interpreter_language (
>   interpreter_id smallint(5) unsigned NOT NULL default '0',
>   language_id smallint(5) unsigned NOT NULL default '0',
>   UNIQUE KEY idx1 (interp_id,lang_id)
> ) TYPE=MyISAM;
>
> Insertion fails if somebody tries to enter a duplicate record.
>
> HTH!
>
>
> ---
> David Mintz
> http://davidmintz.org/
>
>      "You want me to pour the beer, Frank?"
>
>
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