当前位置：首页 > news >正文

MySQL之视图和索引实战

news 来源：原创 2024/9/17 3:11:28

1.新建数据库

mysql> create database myudb5_indexstu;
Query OK, 1 row affected (0.01 sec)
mysql> use myudb5_indexstu;
Database changed

2.新建表

1.学生表student，定义主键，姓名不能重名，性别只能输入男或女，所在系的默认值是“计算机”，结构如下：student(sno 学号，sname 姓名，ssex 性别，sage年龄，sdept所在系)sno为主键

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 (0.03 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)

2.用SQL语句创建课程表

mysql> create table course(cno int primary key not null, cname varchar(20) not null);
Query OK, 0 rows affected (0.01 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)

3.用SQL语句创建选课表

mysql> create table sc(sno int not null, cno varchar(10) primary key not null, score int not null);
Query OK, 0 rows affected (0.01 sec)

mysql> desc sc;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| sno   | int         | NO   |     | NULL    |       |
| cno   | varchar(10) | NO   | PRI | NULL    |       |
| score | int         | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

3.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;
Query OK, 0 rows affected (0.08 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
mysql> show create table course\G
*************************** 1. row ***************************Table: course
Create Table: CREATE TABLE `course` (`cno` int NOT NULL,`cname` varchar(20) NOT NULL,PRIMARY KEY (`cno`),KEY `index_cno` (`cno`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 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> alter table sc add unique index SC_INDEX (sno asc,cno asc);
Query OK, 0 rows affected (0.02 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 student.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 (0.00 sec)Query OK, 0 rows affected (0.01 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