Re: Primary and Foreign Key?

I think i found what i was looking for in the docs:

5.3.4. Primary Keys
Technically, a primary key constraint is simply a combination of a unique
constraint and a not-null constraint.

So i suppose i suppose i would use PRIKARY KEY(peopleid,groupid) to enforce
the UNIQUE NOT NULL constraint in one expression.

Thanks!
-----Original Message-----
From: Wayne Unruh [mailto:waynepunruh@hotmail.com]
Sent: Saturday, September 24, 2005 1:46 AM
To: abanks@insightbb.com; pgsql-novice@postgresql.org
Subject: RE: [NOVICE] Primary and Foreign Key?


In relational databases  A table can have at most one primary key.  However,
you are not required to have a primary key, so I would just have the two
foreign keys in the table PEOPLEGROUPS.

For more information on Constraints see
http://www.postgresql.org/docs/8.0/interactive/ddl-constraints.html

Wayne Unruh

From :     A. Banks <abanks@insightbb.com>
Sent :     Wednesday, September 21, 2005 8:46 PM
To :     <pgsql-novice@postgresql.org>
Subject :     [NOVICE] Primary and Foreign Key?



I have the following related tables:

PEOPLE
--------------
peopleid pkey,
name,
etc


GROUPS
-------------
groupid pkey,
description,
etc


PEOPLEGROUPS
-------------------
peopleid pkey/fkey,
groupid pkey/fkey


What is the CORRECT way (in Postgres) to define the PEOPLEGROUPS table so
that it has both the double primary key AND still acts as a foreign key for
people.peopleid and groups.groupid? Can i specify both or is this not
necessary? Any suggestions would be appreciated.

Thanks!




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