mysql-约束

1.总结

create table user(
	id int primary key auto_increment comment '主键',
    name varchar(10) not null unique comment '姓名',
	age int check( age > 0 && age <= 120 ) comment '年龄',
	status char(1) default '1' comment '状态',
	gender char(1) comment '性别'
) comment '用户表';

---添加外键
alter table emp add constraint fk_emp_dept_id foreign key (dept_id) references dept(id);

--- 删除外键
alter table emp drop foreign key fk_emp_dept_id;