Re: equivalent of mysql's SET type?

On Thu, Mar 10, 2011 at 4:13 PM, Dmitriy Igrishin <dmitigr(at)gmail(dot)com> wrote:
> 2011/3/9 John R Pierce <pierce(at)hogranch(dot)com>
>>
>> On 03/08/11 5:06 PM, Reece Hart wrote:
>>>
>>> I'm considering porting a MySQL database to PostgreSQL. That database
>>> uses MySQL's SET type. Does anyone have advice about representing this type
>>> in PostgreSQL?
>>>
>>> MySQL DDL excerpt:
>>> CREATE TABLE `transcript_variation` (
>>>  `transcript_variation_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
>>>  `transcript_stable_id` varchar(128) NOT NULL,
>>>   ...
>>>  `consequence_type`
>>> set('ESSENTIAL_SPLICE_SITE','STOP_GAINED','STOP_LOST','COMPLEX_INDEL','SPLICE_SITE')
>>> ) ENGINE=MyISAM AUTO_INCREMENT=174923212 DEFAULT CHARSET=latin1;
>>>
>>>
>>
>> why not just have a set of booleans in the table for these individual
>> on/off attributes?   wouldn't that be simplest?
>
> Yes, it might be simplest at first sight.
> But classical solution is relation N - N scales simpler than
> any tricks with bytes.
> Unfortunately, enums and composite types are not extensible. And
> if you need to add yet another option (or remove some option) it
> will be problematic.
> In case of N - N relation you need just use INSERT/DELETE.

actually composite types are fairly workable if you use table instead
of a type (you can drop/add column, etc). in 9.1 you will be able to
do this with vanilla composite type
(http://developer.postgresql.org/pgdocs/postgres/sql-altertype.html).

in typical case I would agree that classic approach of separate
relation is typically the way to go, there are exceptions -- for
example enum gives you inline ordering -- or as in this case where OP
is looking to simplify porting large body of application code.

merlin