MySQL-约束实操

-- -------------------------------------------------约束演示------------------------------------
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';

-- 插入数据
insert into user(name,age,status,gender) values('Tom1',19,'1','男'),('Tom2',25,'0','男');
insert into user(name,age,status,gender) values('Tom3',29,'1','男');

insert into user(name,age,status,gender) values(null,29,'1','男'); #不会插入成功，但是会占用主键
insert into user(name,age,status,gender) values('Tom3',29,'1','男');

insert into user(name,age,status,gender) values('Tom4',80,'1','男');
insert into user(name,age,status,gender) values('Tom5',-1,'1','男');
insert into user(name,age,status,gender) values('Tom5',121,'1','男');

insert into user(name,age,gender) values('Tom5',120,'男');





-- --------------------------------------------约束（外键）----------------------------------------
-- 准备数据
create table dept(
    id int auto_increment comment 'ID' primary key ,
    name varchar(50) not null comment '部门名称'
)comment '部门表';

insert into dept(id, name) values (1,'研发部'),(2,'市场部'),(3,'财务部'),(4,'销售部'),(5,'总经办');


create table emp(
    id int auto_increment comment 'ID' primary key ,
    name varchar(50) not null comment '姓名',
    age int comment '年龄',
    job varchar(20) comment '职位',
    salary int comment '薪资',
    entrtdate date comment '入职时间',
    managerid int comment '直属领导ID',
    dept_id int comment '部门ID'
)comment '员工表';

insert into emp(id, name, age, job, salary, entrtdate, managerid, dept_id)
values (1,'金庸',66,'总裁',88888,'2000-01-01',null,5),
       (2,'张无忌',20,'项目经理',12500,'2005-12-05',1,1),
       (3,'杨逍',33,'开发',8400,'2000-11-03',2,1),
       (4,'韦一笑',48,'开发',11000,'2002-02-05',2,1),
       (5,'常遇春',43,'开发',10500,'2004-09-07',3,1),
       (6,'小昭',19,'程序员鼓励师',6600,'2004-10-12',2,1);

-- 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;



-- 外键的删除和更新行为
alter table emp add constraint fk_emp_dept_id foreign key (dept_id) references dept(id) on update cascade on delete cascade ;

alter table emp add constraint fk_emp_dept_id foreign key (dept_id) references dept(id) on update set null on delete set null ;