Enumeration Type

An enumeration (enum) type is a data type consisting of a static, ordered set of values. They are equivalent to the enum types used in many programming languages. The enumeration type can be a date in a week or a set of status values.

Declaration of Enumeration Types

Enumeration types can be created using the CREATE TYPE command. For example:

1
CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy');

After an enumeration type is created, it can be used in table and function definitions.

1
2
3
4
5
6
7
8
CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy');
CREATE TABLE person (name text, current_mood mood);
INSERT INTO person VALUES ('Moe', 'happy');
SELECT * FROM person WHERE current_mood = 'happy';
 name | current_mood
------+--------------
 Moe  | happy
(1 row)

Sorting

The order of enumeration values is the order of the values listed when the type is created.

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
INSERT INTO person VALUES ('Larry', 'sad');
INSERT INTO person VALUES ('Curly', 'ok');

SELECT * FROM person WHERE current_mood > 'sad';
 name  | current_mood
-------+--------------
 Moe   | happy
 Curly | ok
(2 rows)

SELECT * FROM person WHERE current_mood > 'sad' ORDER BY current_mood;
 name  | current_mood
-------+--------------
 Curly | ok
 Moe   | happy
(2 rows)

SELECT name FROM person WHERE current_mood = (SELECT MIN(current_mood) FROM person);
 name
-------
 Larry
(1 row)

Security of Enumeration Types

Each enumeration data type is independent and cannot be compared with other enumeration types.

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
CREATE TYPE happiness AS ENUM ('happy', 'very happy', 'ecstatic');
CREATE TABLE holidays (num_weeks integer, happiness happiness);
INSERT INTO holidays(num_weeks,happiness) VALUES (4, 'happy');
INSERT INTO holidays(num_weeks,happiness) VALUES (6, 'very happy');
INSERT INTO holidays(num_weeks,happiness) VALUES (8, 'ecstatic');

INSERT INTO holidays(num_weeks,happiness) VALUES (2, 'sad');
ERROR:  invalid input value for enum happiness: "sad"

SELECT person.name, holidays.num_weeks FROM person, holidays
       WHERE person.current_mood = holidays.happiness;
ERROR:  operator does not exist: mood = happiness

If comparison is required, you can use a customized operator or add an explicit type to the query.

1
2
3
4
5
6
 SELECT person.name, holidays.num_weeks FROM person, holidays
       WHERE person.current_mood::text = holidays.happiness::text;
 name | num_weeks
------+-----------
 Moe  |         4
(1 row)

Precautions

Parent topic: Data Types