MySQL:关于列的 NULL 和 NOT NULL
创建一个测试表:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
mysql> use test; Database changed mysql> show tables; Empty set (0.00 sec) mysql> create table people -> ( -> id int, -> name varchar(40), -> sex varchar(10), -> comment varchar(900) -> ); Query OK, 0 rows affected (0.35 sec) mysql> |
看看这时候的表结构:
1 2 3 4 5 6 7 8 9 10 11 12 |
mysql> desc people; +---------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | varchar(40) | YES | | NULL | | | sex | varchar(10) | YES | | NULL | | | comment | varchar(900) | YES | | NULL | | +---------+--------------+------+-----+---------+-------+ 4 rows in set (0.02 sec) mysql> |
可以看到,这个时候是没有非空约束的,所以,你可以有的列不插入值:
[crayon-63e279aa377178[……]