第四次作业

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

alter table student change Sage Sage smallint;

desc student;

2.为Course表中cno课程号字段设置索引，并查看索引

desc course;

create unique index Course_index on Course(Con);

show index from Course;

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

desc sc;

先删除主键

alter table sc primary key;

然后再添加主键

alter table sc add primary key(sno,cno);

创建主键索引索引名为SC_INDEX

create index SC_INDEX on sc(sno asc,cno asc);

show index from sc;

4.创建一视图stu_info,查询全体学生的姓名，性别，课程名，成绩

create view stu_info as select student.sname,student.ssex,course.cname,sc.score from student,sc,course where student.sno=sc.sno and sc.sno=course.cno;

show tables;

desc stu_info;

5.删除所有索引

drop index SC_INDX on sc;

drop index course_index on course;