Upgrading a varchar column to enum type in postgresql

Question

We have a varchar column in a table, that we need to upgrade to enum type.

All the values in the varchar column are valid values in the enumeration. There is no null

Answer 1

You need to define a cast to be used because there is no default cast available.

If all values in the varcharColumn comply with the enum definition, the following should work:

alter table foo 
  ALTER COLUMN varcharColumn TYPE enum_type using varcharColumn::enum_type;

I personally don't like enums because they are quite unflexible. I prefer a check constraint on a varchar column if I want to restrict the values in a column. Or - if the list of values changes often and is going to grow - a good old "lookup table" with a foreign key constraint.

Answer 2

you as well might consider domain type if you dont need the enum ordering property and are offput by missing delete enum value.
Domain types are user-denfiend types + constraints, which makes x out of a selection possible via CHECK & co and as such not so 'unwieldy like enums.

Typical enum is eg log levels, while domain eg email text input validation with the field being present in many tables.

Answer 3

Got it.

ALTER TABLE tableName
   ALTER COLUMN varcharColumn TYPE enum_type
    USING varcharColumn::enum_type

will update it successfully.