Re: how to alter an enum type

["Gurjeet Singh" <singh.gurjeet@xxxxxxxxx>]

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.
-- 
gurjeet[.singh]@EnterpriseDB.com
singh.gurjeet@{ gmail | hotmail | indiatimes | yahoo }.com

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On Dec 24, 2007 12:48 AM, Henrique Pantarotto <henpa@xxxxxxxxxxxx> 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!




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