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Re: Poor-man's enumeration type

From: Michael Glaesemann <grzm(at)myrealbox(dot)com>
To: KeithW(at)NarrowPathInc(dot)com
Cc: PostgreSQL Novice <pgsql-novice(at)postgresql(dot)org>
Subject: Re: Poor-man's enumeration type
Date: 2005-04-26 03:08:53
Message-ID: beac9cea3a272b965cd0925b4f7f080d@myrealbox.com (view raw or flat)
Thread:
Lists: pgsql-novice
On Apr 26, 2005, at 11:52, Keith Worthington wrote:

>    The type "char" (note the quotes) is different
>    from char(1)in that it only uses one byte of
>    storage. It is internally used in the system
>    catalogs as a poor-man's enumeration type.
>
> Is this a SQL standard data type?

No.

> Can I expect this type to be supported in PostgreSQL 'forever'?

I'm not in a position to say, but I do know that "It is internally used 
in the system catalogs" and the system catalogs carry with them the 
explicit warning that they may change--and have changed in the 
past--between releases.

In general, enumeration can be handled by setting up a small table that 
lists allowed values. e.g. (untested),

create table colors ( color text not null unique );

create table houses (
	house_id serial not null unique
	, house_color text not null
	references colors (color) on update cascade on delete cascade
);

Hope this helps.

Michael Glaesemann
grzm myrealbox com


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