How do I "copy" enum values from one enum column to another enum column?

Question

I'm trying to copy the enum values between two columns in a table. The the two enum types have the same enum values:

UPDATE dogs SET breed = breed_old;
...
ERROR:  column "breed" is of type "breed" but expression is of type "breed_old"

I've also tried:

UPDATE dogs SET breed = breed_old::text;
...
ERROR:  column "breed" is of type "breed" but expression is of type text

Any help would be appreciated.

Answer 1

create type foo as enum ('a','b');
create type bar as enum ('a','b');

select 'a'::foo;
┌─────┐
│ foo │
├─────┤
│ a   │
└─────┘

select 'a'::foo::text;
┌──────┐
│ text │
├──────┤
│ a    │
└──────┘

select 'a'::foo::text::bar;
┌─────┐
│ bar │
├─────┤
│ a   │
└─────┘

Or probably more convenient:

update dogs set
    breed = case breed_old
        when 'val1' then 'val1'::breed
        when 'val2' then 'val2'::breed
        ...
    end;