To: Peter Eisentraut <peter_e@gmx.net>
Cc: Rod Taylor <pg@rbt.ca>,
	=?iso-8859-1?q?Mart=EDn_Marqu=E9s?= <martin@bugs.unl.edu.ar>,
	pgsql-sql@postgresql.org
Subject: Re: ENUM like data type 
In-reply-to: <200506292320.32726.peter_e@gmx.net> 
References: <ED4E30DD9C43D5118DFB00508BBBA76EB167AF@neptun.sonorys.at>
	<200506291021.10986.martin@bugs.unl.edu.ar>
	<1120051729.39304.113.camel@home>
	<200506292320.32726.peter_e@gmx.net>
Comments: In-reply-to Peter Eisentraut <peter_e@gmx.net>
	message dated "Wed, 29 Jun 2005 23:20:32 +0200"
Date: Wed, 29 Jun 2005 18:55:59 -0400
Message-ID: <29905.1120085759@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Peter Eisentraut <peter_e@gmx.net> writes:
> Rod Taylor wrote:
>> Indeed. A CHECK constraint on a DOMAIN is an ENUM plus some.

> Not really.  A domain doesn't create a new type.  If you base your enum 
> domains on the text type, as would usually be the case, then nothing 
> stops you from using, say, text concatenation operators and the like.  
> I suppose in practice this won't matter too much, but it can't be 
> called a clean design.  What you'd really need is a way to create a 
> distinct type.  SQL has a feature for that, but PostgreSQL hasn't 
> implemented it.

It's not that hard to make your own type using the builtin textin and
textout functions, and then add just the functions you wish to provide.

			regards, tom lane