MySQL第四次作业

作业题目：

1、创建数据库和表：

mysql> create database mydb15_indexstu;
Query OK, 1 row affected (0.01 sec)

mysql> use  mydb15_indexstu;
Database changed
mysql> create table student(sno int primary key auto_increment, sname varchar(30) not null unique, ssex varchar(2) check (ssex='男' or ssex='女') not null, sage int not null, sdept varchar(10) default '计算机' not null);
Query OK, 0 rows affected (0.05 sec)

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  | int         | NO   |     | NULL    |                |
| sdept | varchar(10) | NO   |     | 计算机  |                |
+-------+-------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

mysql>
mysql> create table course(cno int primary key not null, cname varchar(20) not null);
Query OK, 0 rows affected (0.03 sec)

mysql> desc course;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| cno   | int         | NO   | PRI | NULL    |       |
| cname | varchar(20) | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)

mysql> create table sc(sno int not null, con varchar(10) primary key not null, score int not null);
Query OK, 0 rows affected (0.03 sec)

mysql>
mysql> desc sc;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| sno   | int         | NO   |     | NULL    |       |
| con   | varchar(10) | NO   | PRI | NULL    |       |
| score | int         | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+

2、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

mysql> alter table student modify sage smallint not  null;
Query OK, 0 rows affected (0.11 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    | NO   |     | 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 idx_cno on course(cno);
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show index from course;
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| Table  | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| course |          0 | PRIMARY  |            1 | cno         | A         |           0 |     NULL |   NULL |      | BTREE      |         |               | YES     | NULL       |
| course |          1 | idx_cno  |            1 | cno         | A         |           0 |     NULL |   NULL |      | BTREE      |         |               | YES     | NULL       |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
2 rows in set (0.01 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 index sc_index on sc(sno,con);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> show index from sc;
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| sc    |          0 | PRIMARY  |            1 | con         | A         |           0 |     NULL |   NULL |      | BTREE      |         |               | YES     | NULL       |
| sc    |          1 | sc_index |            1 | sno         | A         |           0 |     NULL |   NULL |      | BTREE      |         |               | YES     | NULL       |
| sc    |          1 | sc_index |            2 | con         | A         |           0 |     NULL |   NULL |      | BTREE      |         |               | YES     | NULL       |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
3 rows in set (0.01 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

mysql> 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.con=c.cno;
Query OK, 0 rows affected (0.01 sec)
mysql> select * from stu_info;
Empty set (0.00 sec)

5、删除所有索引

mysql> drop index idx_cno on course;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> drop index sc_index on sc;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0