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From: aoki@cs.berkeley.edu (Paul M. Aoki)
To: tbalzer@tjb.freinet.de (Thomas Balzer)
Cc: postgres@postgres.Berkeley.EDU
Subject: Re: not null, unique and foreign keys 
Reply-To: aoki@cs.berkeley.edu (Paul M. Aoki)
In-reply-to: Your message of Sun, 21 Aug 1994 18:57:56 +0200 (MET DST) 
	     <m0qcGDU-0001WhC@tjb.freinet.de> 
Date: Mon, 22 Aug 94 10:34:00 -0700
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tbalzer@tjb.freinet.de (Thomas Balzer) writes:
> is there a way to tell Postgres that an attribute in a class is
> unique or not null?

keys don't work.  this may help:

  Date: Mon, 22 Nov 93 09:35:31 +0100
  From: jpv@gavdos.pr.net.CH (Jean-Paul Vetterli)
  To: postgres@postgres.Berkeley.EDU
  Subject: Re: Managing key-value pairs
  
  > From: dunkel@spin.chem.utah.edu (Reinhard Dunkel)
  > Message-Id: <9311220311.AA21809@spin.chem.utah.edu>
  > 
  > [...]
  > I am trying to use Postgres 4.1 (RS/6000-370, AIX 3.2.4) to manage
  > key-value pairs for a graphical user interface. I am embarrassed to
  > admit that I have problems to make this easiest of all database
  > applications work smoothly. I would greatly appreciate any help on the
  > following problems:
  > 
  > PROBLEM 1: I have to enforce that my "param" attribute values (keys)
  > are unique in a database relation.  However, the command "create foo
  > (param=char16, value=text) key (param)\g" is documented in the
  > reference manual but the message "WARN:Nov 21 18:10:13:RelationCreate:
  > KEY not yet supported" sounds discouraging. So before writing a
  > key-value pair I query the database to see if the key is known and
  > then either replace or append the tupel.  This approach takes two
  > database accesses (one second overhead with libpq each). Is there a
  > better way to do this?
  > [...]
  
  One approach to enforce uniqueness is to use rules. 
  Example: 
  
  ---- cut here ----
  #  this is a spog script: %spog -f <thisfile>
  #  it is idempotent 
  #
  #  create key-value table:
  create kv (k = char16,\
  	v = text)
  #
  #  uniqueness *and* integrity:
  define rule kv_r is \
  	on append to kv \
  	where kv.k = new.k or new.k ISNULL \
  	do instead nothing
  #
  #  data:
  append kv (k = "K1", v = "K1's value")
  append kv (k = "K2", v = "K2's value")
  append kv (k = "K3", v = "K3's value")
  append kv (k = "K4", v = "K4's value")
  append kv (k = "K5", v = "etc.")
  ---- cut here ----
  
  I hope this can help.
  
  
  Jean-Paul Vetterli 		
  Route des Pommiers 19		email:	jpv@gavdos.pr.net.CH 		
  CH-1723 Marly			phone:	++77 34 38 27 		
  Switzerland			fax:	++37 46 53 09 

> How to define a foreign key? I can't find anything in the
> documentation of Postgres 4.2. I think they used foreign keys for
> the system tables, aren't they?

nope.
--
  Paul M. Aoki          |  University of California at Berkeley
  aoki@CS.Berkeley.EDU  |  Dept. of EECS, Computer Science Division (#1776) 
                        |  Berkeley, CA 94720-1776

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