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;
