Add value to Postgres enum type, dropping tho...

An enum type in Postgres is a type that can restrict a value to only certain values. It can be defined like this:

create type fruit as Enum ('orange', 'apple');

We can now cast a string to a fruit.

chriserin=# select 'orange'::fruit;
 fruit
--------
 orange

Well... some strings...

chriserin=# select 'rasberry'::fruit;
ERROR:  invalid input value for enum fruit: "rasberry"

It's all good! We can add rasberry to the enum type.

chriserin=# alter type fruit add value 'rasberry';
chriserin=# select 'rasberry'::fruit;
  fruit
----------
 rasberry

Postgres allows you to add values to an enum type, but you can't drop values which is a bit of an inconvenience when creating up/down db migrations like you do in Rails or with a tool like tern.