ENUM

Syntax

ENUM('value1','value2',...) [CHARACTER SET charset_name] [COLLATE collation_name]

Description

An enumeration. A string object that can have only one value, chosen from the list of values 'value1', 'value2', ..., NULL or the special '' error value. In theory, an ENUM column can have a maximum of 65,535 distinct values; in practice, the real maximum depends on many factors. ENUM values are represented internally as integers.

Trailing spaces are automatically stripped from ENUM values on table creation.

ENUMs require relatively little storage space compared to strings, either one or two bytes depending on the number of enumeration values.

NULL and empty values

An ENUM can also contain NULL and empty values. If the ENUM column is declared to permit NULL values, NULL becomes a valid value, as well as the default value (see below). If strict SQL Mode is not enabled, and an invalid value is inserted into an ENUM, a special empty string, with an index value of zero (see Numeric index, below), is inserted, with a warning. This may be confusing, because the empty string is also a possible value, and the only difference if that is this case its index is not 0. Inserting will fail with an error if strict mode is active.

If a DEFAULT clause is missing, the default value will be:

• NULL if the column is nullable;
• otherwise, the first value in the enumeration.

Numeric index

ENUM values are indexed numerically in the order they are defined, and sorting will be performed in this numeric order. We suggest not using ENUM to store numerals, as there is little to no storage space benefit, and it is easy to confuse the enum integer with the enum numeral value by leaving out the quotes.

An ENUM defined as ENUM('apple','orange','pear') would have the following index values:

Examples

CREATE TABLE fruits (
  id INT NOT NULL auto_increment PRIMARY KEY,
  fruit ENUM('apple','orange','pear'),
  bushels INT);

DESCRIBE fruits;
+---------+-------------------------------+------+-----+---------+----------------+
| Field   | Type                          | Null | Key | Default | Extra          |
+---------+-------------------------------+------+-----+---------+----------------+
| id      | int(11)                       | NO   | PRI | NULL    | auto_increment |
| fruit   | enum('apple','orange','pear') | YES  |     | NULL    |                |
| bushels | int(11)                       | YES  |     | NULL    |                |
+---------+-------------------------------+------+-----+---------+----------------+

INSERT INTO fruits
    (fruit,bushels) VALUES
    ('pear',20),
    ('apple',100),
    ('orange',25);

INSERT INTO fruits
    (fruit,bushels) VALUES
    ('avocado',10);
ERROR 1265 (01000): Data truncated for column 'fruit' at row 1

SELECT * FROM fruits;
+----+--------+---------+
| id | fruit  | bushels |
+----+--------+---------+
|  1 | pear   |      20 |
|  2 | apple  |     100 |
|  3 | orange |      25 |
+----+--------+---------+

Selecting by numeric index:

SELECT * FROM fruits WHERE fruit=2;
+----+--------+---------+
| id | fruit  | bushels |
+----+--------+---------+
|  3 | orange |      25 |
+----+--------+---------+

Sorting is according to the index value:

CREATE TABLE enums (a ENUM('2','1'));

INSERT INTO enums VALUES ('1'),('2');

SELECT * FROM enums ORDER BY a ASC;
+------+
| a    |
+------+
| 2    |
| 1    |
+------+

It's easy to get confused between returning the enum integer with the stored value, so we don't suggest using ENUM to store numerals. The first example returns the 1st indexed field ('2' has an index value of 1, as it's defined first), while the second example returns the string value '1'.

SELECT * FROM enums WHERE a=1;
+------+
| a    |
+------+
| 2    |
+------+

SELECT * FROM enums WHERE a='1';
+------+
| a    |
+------+
| 1    |
+------+

See Also

• Data Type Storage Requirements