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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Dunstan <andrew@dunslane.net>
Cc: David G. Johnston <david.g.johnston@gmail.com>
Cc: Matthias Kurz <m.kurz@irregular.at>
Cc: Jim Nasby <Jim.Nasby@bluetreble.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: Alter or rename enum value
Date: Sat, 26 Mar 2016 10:25:41 -0400
Message-ID: <3202.1459002341@sss.pgh.pa.us> (raw)
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Andrew Dunstan <andrew@dunslane.net> writes:
> We don't have the luxury of being able to redesign this as a green 
> fields development.

I'm not actually convinced that we need to do anything.  SQL already has a
perfectly good mechanism for enforcing that a column contains only values
of a mutable set defined in another table --- it's called a foreign key.
The point of inventing enums was to provide a lower-overhead solution
for cases where the allowed value set is *not* mutable.  So okay, if we
can allow certain cases of changing the value set without increasing
the overhead, great.  But when we can't do it without adding a whole
lot of complexity and overhead (and, no doubt, bugs), we need to just
say no.

Maybe the docs about enums need to be a little more explicit about
pointing out this tradeoff.

			regards, tom lane


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