MySQL第四次作业（索引、视图）

要求:

1.修改student 表中年龄(sage)字段属性，数据类型由int 改变为smallint

desc student;
desc  course;
desc  Score;

alter table student modify Sage smallint;

2.为Course表中Cno 课程号字段设置索引,并查看索引

create index index_cno on course(Cno);
show index from course\G

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

create unique index SC_INDEX ON sc(Sno,Cno asc);show index from sc\G

4.创建一视图 stu info,查询全体学生的姓名，性别，课程名，成绩

select  Sname,Ssex,Cname,Score  from student join  sc on student.Sno=sc.Sno join course on sc.Cno=course.Cno;
create or replace view  stu_info as select  Sname,Ssex,Cname,Score  from student join  sc on student.Sno=sc.Sno join course on sc.Cno=course.Cno;

5.删除所有索引

show tables;
+---------------------------+
| Tables_in_mydb15_indexstu |
+---------------------------+
| course                    |
| sc                        |
| stu_info                  |
| student                   |
+---------------------------+
4 rows in set (0.00 sec)
drop index  index_cno  on course;
drop index SC_INDEX on sc;