Re: how to alter an enum type

Here's a possible solution (this may take long time if the table is too
big). The trick is to add a new column with a newly defined datatype, that
picks up values from the old column. Here's the sample psql script (the
session output follows after that):

create type possible_answers as enum ( 'yes' , 'no' );
create table questionnare( Q varchar(256), A possible_answers );
insert into questionnare values( 'dummy Q1', 'yes' );
insert into questionnare values( 'dummy Q2', 'no' );

begin;
create type possible_answers_new as enum ( 'yes' , 'no', 'maybe' );

alter table questionnare rename column A to B;
alter table questionnare add column A possible_answers_new;

update questionnare set A = B::text::possible_answers_new;

alter table questionnare drop column B;
commit;

vacuum full questionnare;

\d questionnare

insert into questionnare values( 'dummy Q3', 'maybe' );

select * from questionnare;

And here's what the session output looks like:

postgres=# create type possible_answers as enum ( 'yes' , 'no' );
CREATE TYPE
postgres=# create table questionnare( Q varchar(256), A possible_answers );
insert into questionnare values( 'dummy Q1', 'yes' );
CREATE TABLE
postgres=# insert into questionnare values( 'dummy Q1', 'yes' );
begin;
INSERT 0 1
postgres=# insert into questionnare values( 'dummy Q2', 'no' );
INSERT 0 1
postgres=#
postgres=# begin;
BEGIN
postgres=# create type possible_answers_new as enum ( 'yes' , 'no', 'maybe'
);
CREATE TYPE
postgres=#
postgres=# alter table questionnare rename column A to B;
ALTER TABLE
postgres=# alter table questionnare add column A possible_answers_new;
ALTER TABLE
postgres=#
postgres=# update questionnare set A = B::text::possible_answers_new;
UPDATE 2
postgres=#
postgres=# alter table questionnare drop column B;
commit;
ALTER TABLE
postgres=# commit;
COMMIT
postgres=#
postgres=# vacuum full questionnare;

VACUUM
postgres=#
postgres=# \d questionnare

Table "public.questionnare"
Column | Type | Modifiers
--------+------------------------+-----------
q | character varying(256) |
a | possible_answers_new |

postgres=#
postgres=# insert into questionnare values( 'dummy Q3', 'maybe' );
INSERT 0 1
postgres=#
postgres=# select * from questionnare;
q | a
----------+-------
dummy Q1 | yes
dummy Q2 | no
dummy Q3 | maybe
(3 rows)

postgres=#

Hope it helps.
--
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Mail sent from my BlackLaptop device
On Dec 24, 2007 12:48 AM, Henrique Pantarotto <henpa(at)terra(dot)com(dot)br> wrote:

> Hi,
>
> I was wondering how can I alter an ENUM type? I have created a table
> like this:
>
> create type possible_answers as enum('yes', 'no');
> create table questions ( question text, answers possible_answers);
> insert into questions values ('Do you like me?', 'yes');
>
> So my question is... How can I change "possible_answers" to enum('yes',
> 'no', 'maybe')?
>
> I tried searching the documentation and mailing list, and I couldn't
> figure this one out.
>
>
> Thanks!
>
>
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
> choose an index scan if your joining column's datatypes do not
> match
>