How to delete an enum type value in postgres?

Question

You delete (drop) enum types like any other type, with DROP TYPE:

DROP TYPE admin_level1;

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Is it possible you're actually asking about how to remove an individual value from an enum type? If so, you can't. It's not supported:

Although enum types are primarily intended for static sets of values, there is support for adding new values to an existing enum type, and for renaming values (see ALTER TYPE). Existing values cannot be removed from an enum type, nor can the sort ordering of such values be changed, short of dropping and re-creating the enum type.

You must create a new type without the value, convert all existing uses of the old type to use the new type, then drop the old type.

E.g.

CREATE TYPE admin_level1 AS ENUM ('classifier', 'moderator');

CREATE TABLE blah (
    user_id integer primary key,
    power admin_level1 not null
);

INSERT INTO blah(user_id, power) VALUES (1, 'moderator'), (10, 'classifier');

ALTER TYPE admin_level1 ADD VALUE 'god';

INSERT INTO blah(user_id, power) VALUES (42, 'god');

-- .... oops, maybe that was a bad idea

CREATE TYPE admin_level1_new AS ENUM ('classifier', 'moderator');

-- Remove values that won't be compatible with new definition
-- You don't have to delete, you might update instead
DELETE FROM blah WHERE power = 'god';

-- Convert to new type, casting via text representation
ALTER TABLE blah 
  ALTER COLUMN power TYPE admin_level1_new 
    USING (power::text::admin_level1_new);

-- and swap the types
DROP TYPE admin_level1;

ALTER TYPE admin_level1_new RENAME TO admin_level1;

Very well written here:

http://blog.yo1.dog/updating-enum-values-in-postgresql-the-safe-and-easy-way/

rename the existing type

ALTER TYPE status_enum RENAME TO status_enum_old;

create the new type

CREATE TYPE status_enum AS ENUM('queued', 'running', 'done');

update the columns to use the new type

ALTER TABLE job ALTER COLUMN job_status TYPE status_enum USING job_status::text::status_enum;

remove the old type

DROP TYPE status_enum_old;

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Possible Errors and Troubleshooting:

• invalid input value for enum {enum name}: "{some value}" - One or more rows have a value ("{some value}") that is not in your new type. You must handle these rows before you can update the column type.
• default for column "{column_name}" cannot be cast automatically to type {enum_name} - The default value for the column is not in your new type. You must change or remove the default value for the column before you can update the column type. Thanks to Philipp for this addition.

If you want delete item of enum type, you must operate on system table of PostgreSQL.

With this command, you can display all the items enum type.

SELECT * FROM pg_enum;

Then check that searched the value is unique. To increase the uniqueness during the removal of rekoru must be passed 'enumtypid' in addition to 'enumlabel'.

This command removes the entry in enum type, where 'unique' is your value.

DELETE FROM pg_enum en WHERE en.enumtypid=124 AND en.enumlabel='unique';

NOTE The example that I described must be used, when by chance we add new value to enum type, and yet we have not used it anywhere in database.

For those who wish to modify the enum values, recreating it seems to be the only viable and safe solution.

It consists in temporarely convert the enum column to a string format, recreate the enum and then reconverting the string column back to the enum type.

Here is an example:

ALTER TABLE your_schema.your_table ALTER COLUMN your_column TYPE varchar(255);
ALTER TABLE your_schema.your_table ALTER COLUMN your_column SET DEFAULT('your_default_enum_value');
DROP TYPE your_schema.your_enum_name;
CREATE TYPE your_schema.your_enum_name AS ENUM ('enum1', 'enum2', 'enum3');
ALTER TABLE your_schema.your_table ALTER your_column DROP DEFAULT;
ALTER TABLE your_schema.your_table ALTER COLUMN your_column TYPE your_schema.your_enum_name USING your_enum_name::your_schema.your_column;
ALTER TABLE your_schema.your_table ALTER COLUMN your_column SET DEFAULT('your_default_enum_value');