what are the different attributes of MySQL ENUM data type?

MySQL ENUM types can be defined with following attributes that affect the allowed values −

• NOT NULL  − In ENUM type, by default NULL values are allowed. To disallow NULL values, we need to use the NOT NULL attribute while describing the ENUM column.
• NULL  − The NULL attribute is a synonym for DEFAULT NULL. The index value for NULL is NULL.
• DEFAULT  − The DEFAULT attribute causes an ENUM data type to have a default value when a value is not specified. In other words, we can say that INSERT statement does not have to include a value for this field because if it does not include then the value following DEFAULT will be inserted. Functions are not allowed in the DEFAULT expression. For ENUM data type the DEFAULT values include NULL and empty string (‘’).

Example

Following example will show the use of these attributes with ENUM data type.

mysql> SET SESSION sql_mode = '';
Query OK, 0 rows affected (0.00 sec)

mysql> Create Table enumtesting(e_value ENUM('a','1')NOT NULL DEFAULT '1',id TINYINT NOT NULL);
Query OK, 0 rows affected (0.23 sec)

mysql>Insert into
enumtesting(e_value,id)values('1','1'),('',2),(NULL,3),('abc',4);
Query OK, 4 rows affected, 3 warnings (0.09 sec)
Records: 4 Duplicates: 0 Warnings: 3

mysql> show warnings;
+---------+------+----------------------------------------------------+
| Level   | Code |  Message                                           |
+---------+------+----------------------------------------------------+
| Warning | 1265 | Data truncated for column 'e_value' at row 2       |
| Warning | 1048 | Column 'e_value' cannot be null                    |
| Warning | 1265 | Data truncated for column 'e_value' at row 4       |
+---------+------+----------------------------------------------------+
3 rows in set (0.00 sec)

mysql> Select * from enumtesting;
+----+---------+
| e_value | id |
+---------+----+
| 1       |  1 |
|         |  2 |
|         |  3 |
|         |  4 |
+---------+----+
4 rows in set (0.00 sec)

mysql> insert into enumtesting(id) values(5);
Query OK, 1 row affected (0.11 sec)

mysql> Select * from enumtesting;
+---------+----+
| e_value | id |
+---------+----+
| 1       | 1 |
|         | 2 |
|         | 3 |
|         | 4 |
| 1       | 5 |
+---------+----+
5 rows in set (0.00 sec)

mysql> select e_value, e_value+0 AS enum_index, id from enumtetsing;
+---------+------------+----+
| e_value | enum_index | id |
+---------+------------+----+
| 1       |          2 |   1|
|         |          0 |   2|
|         |          0 |   3|
|         |          0 |   4|
| 1       |          2 |   5|
+---------+------------+----+
5 rows in set (0.00 sec)

Vanithasree

Published on 20-Feb-2018 06:12:31