1. 修改student 表中年龄(sage)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 (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student;
+-------+-------------+------+-----+-----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+-----------+----------------+
| sno | int | NO | PRI | NULL | auto_increment |
| sname | varchar(30) | NO | UNI | NULL | |
| ssex | varchar(2) | NO | | NULL | |
| sage | smallint | YES | | NULL | |
| sdept | varchar(10) | NO | | 计算机 | |
+-------+-------------+------+-----+-----------+----------------+
5 rows in set (0.00 sec)
2. 为Course表中Cno 课程号字段设置索引,并查看索引
mysql> create index index_cno on course(cno);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
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 index sc_index on sc(sno,cno);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
4. 创建一视图 stu info,查询全体学生的姓名，性别，课程名，成绩
mysql> create 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;
Query OK, 0 rows affected (0.01 sec)
mysql> show tables;
+---------------------------+
| Tables_in_mydb15_indexstu |
+---------------------------+
| course |
| sc |
| stu_info |
| student |
+---------------------------+
4 rows in set (0.00 sec)
5.删除所有索引
mysql> drop index sc_index on sc;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> drop index index_cno on course;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
