作业5/5

作业布置

练习：账号信息表，用户组，主机表，主机组

```python
#用户表
create table user(
id int not null unique auto_increment,
username varchar(20) not null,
password varchar(50) not null,
primary key(username,password)
);

#联合主键

mysql> create table user(
    -> id int not null unique auto_increment,
    -> username varchar(20) not null,
    -> password varchar(50) not null,
    -> primary key(username,password)
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql>

#用户组表
create table usergroup(
id int primary key auto_increment,
groupname varchar(20) not null unique
);

mysql> create table usergroup(
    -> id int primary key auto_increment,
    -> groupname varchar(20) not null unique
    -> );
Query OK, 0 rows affected (0.08 sec)

#主机表
create table host(
id int primary key auto_increment,
ip char(15) not null unique default '127.0.0.1'
);

mysql> create table host(
    -> id int primary key auto_increment,
    -> ip char(15) not null unique default '127.0.0.1'
    -> );
Query OK, 0 rows affected (0.01 sec)

#业务线表
create table business(
id int primary key auto_increment,
business varchar(20) not null unique
);

mysql> create table business(
    -> id int primary key auto_increment,
    -> business varchar(20) not null unique
    -> );
Query OK, 0 rows affected (0.01 sec)

#建关系：user与usergroup

create table user2usergroup(
id int not null unique auto_increment,
user_id int not null,
group_id int not null,
primary key(user_id,group_id),
foreign key(user_id) references user(id),
foreign key(group_id) references usergroup(id)
);

mysql> create table user2usergroup(
    -> id int not null unique auto_increment,
    -> user_id int not null,
    -> group_id int not null,
    -> primary key(user_id,group_id),
    -> foreign key(user_id) references user(id),
    -> foreign key(group_id) references usergroup(id)
    -> );
Query OK, 0 rows affected (0.01 sec)

#建关系：host与business
create table host2business(
id int not null unique auto_increment,
host_id int not null,
business_id int not null,
primary key(host_id,business_id),
foreign key(host_id) references host(id),
foreign key(business_id) references business(id)
);

mysql> create table host2business(
    -> id int not null unique auto_increment,
    -> host_id int not null,
    -> business_id int not null,
    -> primary key(host_id,business_id),
    -> foreign key(host_id) references host(id),
    -> foreign key(business_id) references business(id)
    -> );
Query OK, 0 rows affected (0.01 sec)

#建关系：user与host
create table user2host(
id int not null unique auto_increment,
user_id int not null,
host_id int not null,
primary key(user_id,host_id),
foreign key(user_id) references user(id),
foreign key(host_id) references host(id)
);

mysql> create table user2host(
    -> id int not null unique auto_increment,
    -> user_id int not null,
    -> host_id int not null,
    -> primary key(user_id,host_id),
    -> foreign key(user_id) references user(id),
    -> foreign key(host_id) references host(id)
    -> );
Query OK, 0 rows affected (0.01 sec)

```

练习:

```python
# 班级表
cid caption

# 学生表
sid sname gender class_id
# 老师表
tid tname
# 课程表
cid cname teacher_id
# 成绩表
sid student_id course_id number
```

#班级表
create table class(
        cid int primary key auto_increment,
        caption varchar(20) not null
);

#学生表
create table student(
        sid int primary key auto_increment,
        sname varchar(10) not null,
        gender enum('male','female','others') default 'male',
        class_id int ,
        foreign key(class_id) references class(cid)
        on update cascade
        on delete cascade
);

#老师表
create table teacher(
        tid int primary key auto_increment,
        tname varchar(10) not null
);


#课程表
create table course(
        cid int primary key auto_increment,
        cname char(16) not null,
        teacher_id int,
        foreign key (teacher_id) references teacher(tid)
        on update cascade
        on delete cascade
);

#成绩表
create table score(
                  sid int primary key auto_increment,
                  student_id int ,
                  course_id int,
                  number int,
                  foreign key(student_id) references student(sid)
                  on update cascade
                  on delete cascade,
                  foreign key(course_id) references course(cid)
                  on update cascade
                  on delete cascade
);