Re: [PATCH] Alter or rename enum value

> I started looking at this patch.  I'm kind of unhappy with having *both*
> IF EXISTS and IF NOT EXISTS options on the statement, especially since
> the locations of those phrases in the syntax seem to have been chosen
> with a dartboard.  This feels way more confusing than it is useful.
> Is there really a strong use-case for either option?  I note that
> ALTER TABLE RENAME COLUMN, which is probably used a thousand times
> more often than this will be, has so far not grown either kind of option,
> which sure makes me think that this proposal is getting ahead of itself.

I think they can be useful.  I am writing a lot of migration scripts
for small projects.  It really helps to be able to run parts of them
again.  ALTER TYPE ... ADD VALUE already have IF NOT EXISTS option.  I
don't think we would lose anything to support both of them in here.

The syntax ALTER TYPE ... RENAME VALUE [ IF EXISTS ] ... TO ... [ IF
NOT EXISTS ] looks self-explaining to me.  I haven't confused when I
first saw.  IF EXISTS applying to the old value, IF NOT EXISTS
applying to the new value, are the only reasonable semantics one might
expect from renaming things.  Anybody is interpreting it wrong? or can
think of another syntax?