mysql设置外键（主键依赖）

前置，表一

user;

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

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

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

| id | int(20) | NO | PRI | NULL | auto_increment |

| username | varchar(40) | NO | | NULL | |

| password | varchar(40) | NO | | NULL | |

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

表二

info;

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

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

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

| company_id | int(20) | NO | PRI | NULL | auto_increment |

| company_name | varchar(30) | YES | | NULL | |

| company_address | varchar(50) | YES | | NULL | |

| company_mail | varchar(50) | YES | | NULL | |

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

想使info表中的主键，依赖于user表中的主键，具体操作如下：

alter table info add constraint fk_info_user foreign key(company_id) references user(id);