mysql not null默认值_mysql not null default / default

not null default 说明不能是NULL， 并设置默认值

default 设置默认值 ， 但值也可能是NULL

mysql> create table test (id int, name varchar(10) default 'a', addr varchar(10)

not null default 'b');

Query OK, 0 rows affected (0.04 sec)

mysql> desc test;

+-------+-------------+------+-----+---------+-------+

| Field | Type | Null | Key | Default | Extra |

+-------+-------------+------+-----+---------+-------+

| id | int(11) | YES | | NULL | |

| name | varchar(10) | YES | | a | |

| addr | varchar(10) | NO | | b | |

+-------+-------------+------+-----+---------+-------+

3 rows in set (0.00 sec)

mysql> insert into test id values(1);

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that

corresponds to your MariaDB server version for the right syntax to use near 'id

values(1)' at line 1

mysql> insert into test id values(1);

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that

corresponds to your MariaDB server version for the right syntax to use near 'id

values(1)' at line 1

mysql> insert into test(id) values (1);

Query OK, 1 row affected (0.00 sec)

mysql> insert into test(id) values (1);

Query OK, 1 row affected (0.00 sec)

mysql> insert into test(id) values (1);

Query OK, 1 row affected (0.00 sec)

mysql> select * from test;

+------+------+------+

| id | name | addr |

+------+------+------+

| 1 | a | b |

| 1 | a | b |

| 1 | a | b |

+------+------+------+

3 rows in set (0.00 sec)

mysql> insert into test(id,name) values (1,null);

Query OK, 1 row affected (0.00 sec)

mysql> select * from test;

+------+------+------+

| id | name | addr |

+------+------+------+

| 1 | a | b |

| 1 | a | b |

| 1 | a | b |

| 1 | NULL | b |

+------+------+------+

4 rows in set (0.00 sec)

mysql> insert into test(id,addr) values (1,null);

ERROR 1048 (23000): Column 'addr' cannot be null

mysql>