MYSQL库表操作的基础操作4

一、新建数据库

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

二、新建表

1、学生表 student，定义主键，姓名不能重复，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 (0.01 sec)

2、用 SQL 语句创建课程表Course (Cno 课程号，Cname 课程名) Cno 为主键

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SC (Sno 学号，Cno 课程号，Score 成绩) Sno,Cno 为主键

mysql> create table SC(
    -> sno int not null,
    -> cno varchar(10) not null,
    -> score int not null,
    -> primary key (sno,cno)
    -> );
Query OK, 0 rows affected (0.02 sec)
 
mysql> desc sc;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| sno   | int         | NO   | PRI | NULL    |       |
| cno   | varchar(10) | NO   | PRI | NULL    |       |
| score | int         | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

三、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 column sage smallint;
Query OK, 0 rows affected (0.06 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 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 | index_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,cno);
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 | sno         | A         |           0 |     NULL |   NULL |      | BTREE      |         |               | YES     | NULL       |
| sc    |          0 | PRIMARY  |            2 | cno         | 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 | cno         | A         |           0 |     NULL |   NULL |      | BTREE      |         |               | YES     | NULL       |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
4 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.Cno = 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 index_cno on course;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0
 
mysql> drop index SC_INDEX on SC;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0