From: | Patrick Welche <prlw1(at)newn(dot)cam(dot)ac(dot)uk> |
---|---|
To: | PostgreSQL General <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: FOREIGN KEY questions |
Date: | 2000-09-10 11:46:43 |
Message-ID: | 20000910124643.D21418@quartz.newn.cam.ac.uk |
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Lists: | pgsql-general |
On Sun, Sep 10, 2000 at 12:43:08AM -0400, Neil Conway wrote:
> I'm having a bit of difficulty understanding the correct usage of
> foreign keys (I've never used them before, excuse my ignorance).
> Here's a situation where I'm trying to figure out how/if they
> should be used:
>
> One database has a group of tables with intereferential data.
> For example:
>
> CREATE TABLE messages (
> /* ... */
> poster INT4 NOT NULL,
> thread INT4 NOT NULL
> );
>
> CREATE TABLE users (
> id serial
> /* ... */
> );
>
> CREATE TABLE threads (
> id serial
> /* ... */
> );
Something like
CREATE TABLE messages (
/* ... */
poster INT4 NOT NULL REFERENCES users,
thread INT4 NOT NULL REFERENCES threads,
);
CREATE TABLE users (
id serial PRIMARY KEY
/* ... */
);
CREATE TABLE threads (
id serial PRIMARY KEY
/* ... */
);
cf. Bruce's book:
http://www.postgresql.org/docs/aw_pgsql_book/node156.html
Cheers,
Patrick
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