mysql 建立表之间关系 练习 2

创建数据库db6

create database db6 charset=utf8;

user db6;

# 创建班级表

mysql> create table class(cid int primary key auto_increment,caption varchar(50) not null unique);
Query OK, 0 rows affected (0.15 sec)
 
mysql> select * from class;
Empty set (0.00 sec)
 
mysql> insert into class(caption) values('三年二班'),('一年三班'),('三年一班');
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0
 
mysql> select * from class;
+-----+--------------+
| cid | caption      |
+-----+--------------+
|   2 | 一年三班     |
|   3 | 三年一班     |
|   1 | 三年二班     |
+-----+--------------+
3 rows in set (0.00 sec)

# 创建老师表

mysql> create table teacher(tid int primary key auto_increment,tname varchar(50) not null);
Query OK, 0 rows affected (0.11 sec)
 
mysql> insert into teacher(tname) values('李老师'),('吴老师'),('陈老师');
Query OK, 3 rows affected (0.12 sec)
Records: 3  Duplicates: 0  Warnings: 0
 
mysql> select * from teacher;
+-----+-----------+
| tid | tname     |
+-----+-----------+
|   1 | 李老师    |
|   2 | 吴老师    |
|   3 | 陈老师    |
+-----+-----------+
3 rows in set (0.00 sec)

多对一关系建表

# 学生表与班级表建立关系

创建学生表

mysql> create table student(
sid int primary key auto_increment,
sname varchar(20) not null,
gender enum('男','女') not null,
class_id int not null,
foreign key(class_id) references class(cid)
on delete cascade
on update cascade);
Query OK, 0 rows affected (0.06 sec)

mysql> insert into student(sname,gender,class_id) values('小红','女',1),('小李','女',1),('小刚','男',2);
Query OK, 3 rows affected (0.36 sec)
Records: 3  Duplicates: 0  Warnings: 0
 
mysql> select * from student;
+-----+--------+--------+----------+
| sid | sname  | gender | class_id |
+-----+--------+--------+----------+
|   1 | 小红   | 女     |        1 |
|   2 | 小李   | 女     |        1 |
|   3 | 小刚   | 男     |        2 |
+-----+--------+--------+----------+
3 rows in set (0.00 sec)

# 老师表和课程表建立关系

创建课程表

mysql> create table course(
cid int primary key auto_increment,
cname varchar(20) not null,
tearch_id int not null,
foreign key(tearch_id) references teacher(tid) 
on delete cascade
on update cascade);
Query OK, 0 rows affected (0.12 sec

插入记录 并查询

mysql> insert into course(cname,tearch_id) values('生物',1),('体育',1),('物理',2);
Query OK, 3 rows affected (0.11 sec)
Records: 3  Duplicates: 0  Warnings: 0
 
mysql> select * from course;
+-----+--------+-----------+
| cid | cname  | tearch_id |
+-----+--------+-----------+
|   1 | 生物   |         1 |
|   2 | 体育   |         1 |
|   3 | 物理   |         2 |
+-----+--------+-----------+
3 rows in set (0.00 sec)

建立多对多关系

# 建立一张score表 与 学生表 课程表建立关系

mysql> create table score(
sid int not null unique auto_increment,
student_id int not null,
corse_id int not null,
number char(16) not null,
foreign key(student_id) references student(sid)
on delete cascade
on update cascade,
foreign key(corse_id) references course(cid)
on delete cascade
on update cascade,
primary key(student_id,corse_id)
);

插入记录

mysql> insert into score(student_id,corse_id,number) values(1,1,''),(1,2,''),(2,2,'');
Query OK, 3 rows affected (0.70 sec)
Records: 3  Duplicates: 0  Warnings: 0
 
mysql> select * from score;
+-----+------------+----------+--------+
| sid | student_id | corse_id | number |
+-----+------------+----------+--------+
|   1 |          1 |        1 | 60     |
|   2 |          1 |        2 | 59     |
|   3 |          2 |        2 | 100    |
+-----+------------+----------+--------+
3 rows in set (0.00 sec)