如何在具有 NOT NULL 约束的 MySQL 表的字符类型列中插入 NULL 关键字作为值?
很可能将 NULL 关键字作为值插入到具有 NOT NULL 约束的字符类型列中,因为 NULL 本身就是一个值。下面的示例将展示它 -
mysql> Describe test2G *************************** 1. row *************************** Field: id Type: int(11) Null: NO Key: Default: NULL Extra: *************************** 2. row *************************** Field: NAME Type: varchar(20) Null: NO Key: Default: NULL Extra: 2 rows in set (0.03 sec)
现在,借助以下查询,我们可以在“Name”列中插入 NULL 作为值。
mysql> Insert into test2 values(2, 'NULL'); Query OK, 1 row affected (0.06 sec) mysql> select * from test2; +----+--------+ | id | NAME | +----+--------+ | 1 | Gaurav | | 2 | NULL | +----+--------+ 2 rows in set (0.00 sec) 登录后复制
mysql> delete from test2 where name IS NULL; Query OK, 0 rows affected (0.00 sec) 登录后复制
mysql> select * from test2; +----+--------+ | id | NAME | +----+--------+ | 1 | Gaurav | | 2 | NULL | +----+--------+ 2 rows in set (0.00 sec) mysql> delete from test2 where name = 'NULL'; Query OK, 1 row affected (0.09 sec) 登录后复制
mysql> select * from test2; +----+--------+ | id | NAME | +----+--------+ | 1 | Gaurav | +----+--------+ 1 row in set (0.00 sec)登录后复制