Adding a new value to an existing ENUM Type

Question

I have a table column that uses an enum type. I wish to update that enum type to have an additional possible value. I don\'t want to delete any exi

Answer 1

Updating pg_enum works, as does the intermediary column trick highlighted above. One can also use USING magic to change the column's type directly:

CREATE TYPE test AS enum('a', 'b');
CREATE TABLE foo (bar test);
INSERT INTO foo VALUES ('a'), ('b');

ALTER TABLE foo ALTER COLUMN bar TYPE varchar;

DROP TYPE test;
CREATE TYPE test as enum('a', 'b', 'c');

ALTER TABLE foo ALTER COLUMN bar TYPE test
USING CASE
WHEN bar = ANY (enum_range(null::test)::varchar[])
THEN bar::test
WHEN bar = ANY ('{convert, these, values}'::varchar[])
THEN 'c'::test
ELSE NULL
END;

As long as you've no functions that explicitly require or return that enum, you're good. (pgsql will complain when you drop the type if there are.)

Also, note that PG9.1 is introducing an ALTER TYPE statement, which will work on enums:

http://developer.postgresql.org/pgdocs/postgres/release-9-1-alpha.html