5.5作业

练习：账号信息表，用户组，主机表，主机组

#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)
);

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

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

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

#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)
);

#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)
);

#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)
);

练习:

# 班级表
cid	caption
create table class(
cid int primary key auto_increment,
caption char(16) not null
);
# 学生表
sid sname gender class_id
create table class(
sid int primary key auto_increment,
sname char(16) not null,
gender enum('male','female','others'),
class_id  int ,
foreign key(class_id) references class(cid)
on update cascade    
on delete cascade    
);

# 老师表
tid	tname
create table teacher(
tid int primary key auto_increment,
tname char(16) not null   
);
# 课程表
cid	cname	teacher_id
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
sid	student_id course_id number
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    
)