Re: ALTER composite type does not work, but ALTER TABLE which ROWTYPE is used as a type - works fine

On Wed, Dec 10, 2008 at 9:05 AM, Alvaro Herrera
<alvherre@commandprompt.com> wrote:
> Merlin Moncure escribió:
>> >>  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
>> >> OK, so what should the TODO item be?
>> On Wed, Dec 10, 2008 at 7:44 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>> > Allow ALTER TYPE to add, rename, change the type of, and drop columns?
>>
>> That's probably the consensus view.  Personally, I think creating
>> composite types through 'create type as' was a mistake...we probably
>> should have gone through create table instead with some special syntax
>> for storage-less tables aka composite types.
>
> I disagree that CREATE TABLE should be (or should have been) used to
> create types.  Someday we might need to expand the work we do for that
> case in a different direction than tables, and we would be stuck.

But, tables _are_ types, particularly in relational parlance.  In
fact, postgresql's older, more relational terms (tuples and such) are
coming from that perspective, although I admit that's mostly
irrelevant now.  I think we are more stuck now, having to re-implement
many things alter table does in 'alter type (as)???'.  It's a mess.
What if we want to add check constraints to composite types?

> Also, for tables we create files, we generate statistics, we compute
> relfrozenxid, we call vacuum on, and so on and so forth.  We do none of
> these things on types.

Those things are what come with 'storage' so if you are defining a
type with no storage mechanism you could possibly skip those things.

> In fact, types are not in pg_class at all.

incorrect!!  composite types are in pg_class (relkind='c').  That
actually knida confirms what I'm saying, composite types were added in
a confusing overlay over the 'create type' command, which is something
completely different.  create type means two completely different
things depending on a minor grammar change...gah! :-)

I still stand by by statement...create table should have allowed you
to create a composite type as we do it with create type as today...and
(perhaps) storage (relfrozenxid etc.) could be added or removed with
alter table.

merlin