How to delete an enum type value in postgres?

Question

How do I delete an enum type value that I created in postgresql?

create type admin_level1 as enum(\'classifier\', \'moderator\', \'god\');

Answer 1

The programmatic way to do this is as follows. The same general steps as given in https://stackoverflow.com/a/47305844/629272 are appropriate, but those are more manual than made sense for my purposes (writing an alembic down migration). my_type, my_type_old, and value_to_delete, should, of course, be changed as appropriate.

1. Rename your type.

   ALTER TYPE my_type RENAME TO my_type_old;
   

2. Create a new type with the values from your old type, excluding the one you want to delete.

   DO $$
   BEGIN
       EXECUTE format(
           'CREATE TYPE my_type AS ENUM (%s)',
           (
               SELECT string_agg(quote_literal(value), ',')
               FROM unnest(enum_range(NULL::my_type_old)) value
               WHERE value <> 'value_to_delete'
           )
       );
   END $$;
   

3. Change all existing columns which use the old type to use the new one.

   DO $$
   DECLARE
       column_data record;
       table_name varchar(255);
       column_name varchar(255);
   BEGIN
       FOR column_data IN
           SELECT cols.table_name, cols.column_name
               FROM information_schema.columns cols
               WHERE udt_name = 'my_type_old'
       LOOP
           table_name := column_data.table_name;
           column_name := column_data.column_name;
           EXECUTE format(
               '
                   ALTER TABLE %s
                   ALTER COLUMN %s
                   TYPE my_type
                   USING %s::text::my_type;
               ',
               table_name, column_name, column_name
           );
       END LOOP;
   END $$;
   

4. Delete the old type.

   DROP TYPE my_type_old;