表定义
学生表：Student (Sno, Sname, Ssex , Sage, Sdept)
学号，姓名，性别，年龄，所在系 Sno为主键
课程表：Course (Cno, Cname,)
课程号，课程名 Cno为主键
学生选课表：SC (Sno, Cno, Score)
学号，课程号，成绩 Sno,Cno为主键
练习
1.用SQL语句创建学生表student，定义主键，姓名不能重名，性别只能输入男或女，所在系的默认值是 “计算机”。
mysql> create table Student(
-> Sno int primary key comment '学号',
-> Sname varchar(50) unique comment '姓名',
-> Ssex enum('男','女') comment '性别',
-> Sage int comment '年龄',
-> Sdept varchar(50) default '计算机' comment '所在系'
-> );
Query OK, 0 rows affected (0.03 sec)
mysql> desc Student;
+-------+-------------------+------+-----+-----------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------------+------+-----+-----------+-------+
| Sno | int | NO | PRI | NULL | |
| Sname | varchar(50) | YES | UNI | NULL | |
| Ssex | enum('男','女') | YES | | NULL | |
| Sage | int | YES | | NULL | |
| Sdept | varchar(50) | YES | | 计算机 | |
+-------+-------------------+------+-----+-----------+-------+
5 rows in set (0.04 sec)
2.修改student 表中年龄（age）字段属性，数据类型由int 改变为smallint。
mysql> alter table Student modify Sage smallint;
Query OK, 0 rows affected (0.08 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc Student;
+-------+-------------------+------+-----+-----------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------------+------+-----+-----------+-------+
| Sno | int | NO | PRI | NULL | |
| Sname | varchar(50) | YES | UNI | NULL | |
| Ssex | enum('男','女') | YES | | NULL | |
| Sage | smallint | YES | | NULL | |
| Sdept | varchar(50) | YES | | 计算机 | |
+-------+-------------------+------+-----+-----------+-------+
5 rows in set (0.00 sec)
3.为SC表建立按学号（sno）和课程号（cno）组合的升序的主键索引，索引名为SC_INDEX 。
mysql> create table SC(
-> Sno int comment '学号',
-> Cno int comment '课程号',
-> Score int comment '成绩',
-> primary key SC_INDEX(Sno,Cno)
-> );
Query OK, 0 rows affected (0.03 sec)
mysql> desc SC;
+-------+------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------+------+-----+---------+-------+
| Sno | int | NO | PRI | NULL | |
| Cno | int | NO | PRI | NULL | |
| Score | int | YES | | NULL | |
+-------+------+------+-----+---------+-------+
3 rows in set (0.00 sec)
4.创建一视图 stu_info,查询全体学生的姓名，性别，课程名，成绩。
(1)创建课程表：
mysql> create table Course(
-> Con int comment '课程号',
-> Cname varchar(50) comment '课程名'
-> );
Query OK, 0 rows affected (0.05 sec)
mysql> desc Course;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| Con | int | YES | | NULL | |
| Cname | varchar(50) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
(2)给学生表、课程表、学生选课表插入数据
a.学生表(Student)
mysql> insert into Student values
-> (1, '张三', '男', 20, '计算机'),
-> (2, '李四', '女', 22, '计算机'),
-> (3, '王五', '男', 21, '数学'),
-> (4, '赵六', '女', 23, '数学'),
-> (5, '孙七', '男', 24, '英语');
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0\
mysql> select * from Student;
+-----+--------+------+------+-----------+
| Sno | Sname | Ssex | Sage | Sdept |
+-----+--------+------+------+-----------+
| 1 | 张三 | 男 | 20 | 计算机 |
| 2 | 李四 | 女 | 22 | 计算机 |
| 3 | 王五 | 男 | 21 | 数学 |
| 4 | 赵六 | 女 | 23 | 数学 |
| 5 | 孙七 | 男 | 24 | 英语 |
+-----+--------+------+------+-----------+
5 rows in set (0.00 sec)
b.课程表(Course)
mysql> insert into Course values (1, '云原生'),(1, '云原生'),(2, '高等数学'),(2, '高等数学'),(3, '英语');
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select * from Course;
+------+--------------+
| Con | Cname |
+------+--------------+
| 1 | 云原生 |
| 1 | 云原生 |
| 2 | 高等数学 |
| 2 | 高等数学 |
| 3 | 英语 |
+------+--------------+
5 rows in set (0.01 sec)
c.学生选课(SC)
mysql> insert into SC values (1, 1, 90),(2, 1, 85),(3, 2, 92),(4, 2, 88),(5, 3, 95);
Query OK, 5 rows affected (0.03 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select * from SC;
+-----+-----+-------+
| Sno | Cno | Score |
+-----+-----+-------+
| 1 | 1 | 90 |
| 2 | 1 | 85 |
| 3 | 2 | 92 |
| 4 | 2 | 88 |
| 5 | 3 | 95 |
+-----+-----+-------+
5 rows in set (0.00 sec)
文章来源：https://www.toymoban.com/news/detail-795948.html
(3)创建stu_info视图。
mysql> create view v_S_SC_C as
-> select distinct Sname 姓名,Ssex 性别,Cname 课程名,Score 成绩 from Student S
-> inner join SC on S.Sno = SC.Sno
-> inner join Course C on SC.Cno = C.Con;
Query OK, 0 rows affected (0.04 sec)
mysql> desc v_S_SC_C;
+-----------+-------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-------------------+------+-----+---------+-------+
| 姓名 | varchar(50) | YES | | NULL | |
| 性别 | enum('男','女') | YES | | NULL | |
| 课程名 | varchar(50) | YES | | NULL | |
| 成绩 | int | YES | | NULL | |
+-----------+-------------------+------+-----+---------+-------+
4 rows in set (0.03 sec)
mysql> select * from v_S_SC_C;
+--------+--------+--------------+--------+
| 姓名 | 性别 | 课程名 | 成绩 |
+--------+--------+--------------+--------+
| 张三 | 男 | 云原生 | 90 |
| 李四 | 女 | 云原生 | 85 |
| 王五 | 男 | 高等数学 | 92 |
| 赵六 | 女 | 高等数学 | 88 |
| 孙七 | 男 | 英语 | 95 |
+--------+--------+--------------+--------+
5 rows in set (0.00 sec)
文章来源地址https://www.toymoban.com/news/detail-795948.html
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