How to delete an enum type value in postgres?

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

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

E.g. I want to remove moderator from the list.

I can't seem to find anything on the docs.

I'm using Postgresql 9.3.4.

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

DROP TYPE admin_level1;

---

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;

---

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');

Use following query to Delete ENUM value from Postgresql type

DELETE FROM pg_enum
WHERE enumlabel = 'moderator'
AND enumtypid = ( SELECT oid FROM pg_type WHERE typname = 'admin_level1');

Just info for what's type and what's value

DELETE FROM pg_enum
WHERE enumlabel = 'ENUM_VALUE'
AND enumtypid = ( SELECT oid FROM pg_type WHERE typname = 'ENUM_TYPE')

You should change existing values to other. For that if you need to add new value, then use:

ALTER TYPE **ENUM_TYPE** ADD VALUE '**ENUM_VALUE2**'; 

Before deleting, update type value to new type value or existing value.

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;

My solution starts from the fact that I don't have permissions in my scenario to perform DELETE FROM pg_enum as I'm getting a permissions error.

Starting from other replies, I created a generic function that can be used to remove a single value from a enum, supporting the update value to release the use of given value

-- https://stackoverflow.com/a/62444685
-- https://stackoverflow.com/a/51073579
create or replace function remove_enum_value(
	type_name text, 		-- Name of the type where you need to remove a value from
	value_to_delete text,	-- Specific value of the given type you want to remove
	value_fallback text, 	-- Which new value columns will have instead of the value deleted
	column_default text		-- DEFAULT value for the column after type alteration (DEFAULT need to be disabled before changing type, https://stackoverflow.com/a/41149789)
)
RETURNS VOID AS $body$

declare 
	-- Used as temporary type
	_type_name_tmp text := type_name || '_tmp_' || floor(extract(epoch from now()) * 1000);

	-- Used to store statements to execute
	_sql text;

	-- Used to loop tables and switch type from current to temporary
	_column_data record;
    _table_name varchar(255);
    _column_name varchar(255);
   
begin	
	
	--------------------------------------------------------------------------------------------------------------
	
	-- Check: required inputs
	if type_name is null
	then
		raise exception 'Parameter type_name is null';
	end if;
	if value_to_delete is null
	then
		raise exception 'Parameter value_to_delete is null';
	end if;
	
	-- Check: type exists
	IF not EXISTS (SELECT 1 FROM pg_type WHERE typname = type_name) THEN
		raise info 'Type %s does not exists', type_name;
		return;
    END IF;
	
	-- Check: value to delete exists
	if not exists(
		select * 
		FROM pg_enum -- check existing of value to delete
		WHERE enumtypid = (select oid from pg_type where typName=cast(type_name as varchar) limit 1) and enumlabel=cast(value_to_delete as varchar)
	)
	then 
		raise info 'Value to delete % does not exists in type %s', value_to_delete, type_name;
		return;
	end if;
		
	-- Check: fallback value is provided and exists
	if value_fallback is not null and not exists(
		select * 
		FROM pg_enum -- check existing of value to delete
		where
			enumtypid = (select oid from pg_type where typName=cast(type_name as varchar) limit 1)
			and enumlabel=cast(value_fallback as varchar)
	)
	then 
		raise info 'Fallback value % does not exists in type %s', value_fallback, type_name;
		return;
	end if;

	-- Check values are different
	if value_fallback = value_to_delete
	then
		raise info 'Value to delete %s is the same as fallback value %', value_to_delete, value_fallback;
		return;
	end if;

	raise info 'Checks passed, ready to process!';

	--------------------------------------------------------------------------------------------------------------
		
   	-- Retrieve current values of type
   	_sql := format('
   		SELECT string_agg(quote_literal(value), '','')
        FROM unnest(enum_range(NULL::%s)) value
        WHERE value <> ''%s''
	', type_name, value_to_delete);
	raise info '%', _sql;
	execute _sql into _sql;

	-- Create temporary enum
	_sql := format(
        'CREATE TYPE %s AS ENUM (%s)',
        _type_name_tmp,
        _sql
    );
   	raise info '%', _sql;
	execute _sql;

	-- Rename all values from value that need to be deleted to new value (selecting all tables with schemas which has column with enum relation)
    for _column_data in (
    	select
    		concat(c.table_schema,'.',c.table_name ) as table_name,
    		c.column_name
        FROM information_schema.columns c
        where
        	c.udt_name = cast(type_name as varchar)
        	and c.table_schema=c.udt_schema 
        	and data_type = 'USER-DEFINED'
    )
    LOOP
        _sql:= format('UPDATE %1$s set %2$s = %3$L where %2$s=%4$L', _column_data.table_name, _column_data.column_name, value_fallback, value_to_delete);
        raise info 'Update by looping: %', _sql;
        EXECUTE _sql;
    END LOOP;

	-- Switch type from current to temporary
    FOR _column_data in (
        SELECT cols.table_name, cols.column_name
        FROM information_schema.columns cols
        WHERE udt_name = type_name
    )
    LOOP
        _table_name := _column_data.table_name;
        _column_name := _column_data.column_name;
        _sql := format(
            '
                ALTER TABLE %s
					ALTER COLUMN %s DROP DEFAULT,
                	ALTER COLUMN %s TYPE %s USING %s::text::%s,
					ALTER COLUMN %s SET DEFAULT %s;
            ',
            _table_name, 
            _column_name, 
            _column_name, _type_name_tmp, _column_name, _type_name_tmp,
            _column_name, (case when column_default is null then null else '''' || column_default || '''::' || _type_name_tmp end)
        );
       
		raise info '%', _sql;
		execute _sql;
    END LOOP;
   
   	-- Drop previous type
   	_sql := format('DROP TYPE %s;', type_name);
	raise info '%', _sql;
   	execute _sql;
   	
	-- Rename type to previous name
	_sql := format('ALTER TYPE %s RENAME TO %s;', _type_name_tmp, type_name);
	raise info '%', _sql;
   	execute _sql;
   	   
END $body$
LANGUAGE plpgsql;

It's not possible to delete individual value from ENUM, the only possible solution is to DROP and recreate ENUM with needed values.

Had the same problem in v.10. postgres. Deletion requires certain procedures, and if the sequence is not correct, then there will even be a chance of the table being locked for reading.

Wrote a convenient script to delete. Already proven several times its performance. However, this procedure involves replacing the deleted value with a new one (it can be NULL if the table field allows this).

To use, you just need to fill in 3 values.

DO $$
DECLARE
    enumTypeName VARCHAR := 'enum_name'; -- VALUE #1, set yor value!
    enumOldFieldValue varchar := 'old_enum_value'; -- VALUE #2, enum value which have to be deleted
    enumNewFieldValue varchar := null; -- VALUE #3, which new value must be instead of deleted
    sql varchar:='';
    rec record;
BEGIN
    raise info 'Check on old and new enum values.';
    IF exists(select * FROM pg_enum -- check existing of OLD enum value
              WHERE enumtypid = (select oid from pg_type where typName=cast(enumTypeName as varchar) limit 1) and enumlabel=cast(enumOldFieldValue as varchar))
      AND
       (exists(select *
               FROM pg_enum -- check existing of NEW enum value
               WHERE enumtypid = (select oid from pg_type where typName = cast(enumTypeName as varchar) limit 1)
                 and enumlabel = cast(enumNewFieldValue as varchar))
           OR
        enumNewFieldValue IS NULL)
        THEN
            raise info 'Check passed!';

            -- selecting all tables with schemas which has column with enum relation
            create temporary table tmp_table_names
             as SELECT concat(c.table_schema,'.',c.table_name ) as table_name, c.column_name
                FROM information_schema.columns c
                WHERE c.udt_name = cast(enumTypeName as varchar)
                  and c.table_schema=c.udt_schema and data_type = 'USER-DEFINED';

            -- if we have table(s) that uses such enum
            if exists(select * from tmp_table_names)
                then
                    FOR rec in (select table_name, column_name from tmp_table_names) LOOP
                        sql:= format('UPDATE %1$s set %2$s = %3$L where %2$s=%4$L',rec.table_name, rec.column_name, enumNewFieldValue, enumOldFieldValue);
                        raise info 'Update by looping: %', sql;
                        EXECUTE sql;
                    END LOOP;
            end if;

            -- just after changing all old values in all tables we can delete old enum value
            sql := format('DELETE FROM pg_enum WHERE enumtypid = (select oid from pg_type where typName=%1$L limit 1) and enumlabel=%2$L',enumTypeName,enumOldFieldValue);
            raise info 'Delete enum value: %', sql;
            EXECUTE sql;

            drop table  tmp_table_names;
        ELSE
            raise info 'Old or new enum values is missing.';
    end if;
END $$;

1. List item

if your dataset is not so big you can dump with --column-inserts edit the dump with a text editor, remove the value and re-import the dump