MySQL处理表

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

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;

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

ALTER TABLE SC ADD PRIMARY KEY(sno，cno);

ALTER TABLE SC DROP PRIMARY KEY;

ALTER TABLE SC ADD CONSTRAINT SC_INDEX PRIMARY KEY(sno , cno);

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 S.sname,S.ssex,C.cname, SC.score

FROM Student s

JOIN SC ON S.sno = SC.sno

JOIN Course C ON SC.cno = C.cno;

SELECT * FROM stu_info;

5.删除所有索引

ALTER TABLE SC DROP PRIMARY KEY;

DROP INDEX index_Cno ON Course;