mysql启动和常用语法实战回顾

1.前言

回顾完pandas，紧接着也罢把mysql也回顾回顾吧。

2.mysql启动

打开cmd，输入：net start mysql80，其中80是之前你安装mysql时设置的服务器的名称，
如果报如下的错，就说明时cmd的权限不够，要打开cmd所在的目录，更改为管理员模式，并将更改后的cmd文件复制到c:/windows下，并重命名为cmdd，以后运行cmd就通过win+r然后输入cmdd就OK了，如果你用原来的cmd还是会报错哦。

启动成功为：

附带一句：这个mysql启动可以通过如下的按钮直接完成：

停止服务器：

net stop mysql80

停止与登录服务器账户密码后再退出的效果一样：

exit;

3.登录服务器

4.开始正式探索sql语句

对下面基本的语句不做过多的解释，只对比较难的做解释。

（1）show databases;

（2）use 某个数据库;

（3）show tables;

（4）create table student(name varchar(10));

其中的10表示的是最多10个汉字哦，再mysql中，一个汉字占用3个字节。

（5）desc student;或者describe student;

显示student表的配置结构。

（6）select * from student;

*表示没有具体的查询对象，返回所有的内容。

（7）insert into student values('张三');

（8）update student set name='王四';

（9）delete from student where name='王四';

（10）drop table student;

（11）create table student(name varchar(10), id int); alter table student add primary key(id);desc student;

+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| name  | varchar(10) | YES  |     | NULL    |       |
| id    | int         | NO   | PRI | NULL    |       |
+-------+-------------+------+-----+---------+-------+

还可以通过下面的操作达到同样的效果：

alter table student modify id int primary key;

有一点需要注意的是：主键设置了并不会在表中有所显示，除非用desc。按理说应该是会放在最前面的一列才更直观。

删除所有的primary key:

alter table student drop primary key;

（12）create table student(name varchar(10), unique(name));

创建唯一的primary key。

（13）alter table student drop index name;

删除唯一的primary key。

（14）create table student(name varchar(10) not null);

非空约束。

（15）alter table student modify name varchar(10);

删除非空约束， 通过modify间接去掉了原来的约束。

（16）create table student(name varchar(10) default '张三', id int);

默认约束，但这个默认值有用吗？好像有没有都没啥影响吧。

（17）alter table student modify name varchar(10);

删除默认约束。

（18）create table class(name varchar(10), id int primary key);create table student(name varchar(10), id int primary key, class_id int, foreign key(class_id) references class(id));

主表是：class
副表是：student
当主表有数据被副表利用时，主表不能被删除
主表中没有的数值，在副表中不能使用

（19）1NF(范式)

（20）2NF

（21）3NF

（2）3NF

5.实际项目

这个项目目的在于复习。

(1) 建表

# 创建数据库data1
CREATE DATABASE data1;

# 使用数据库data1
USE data1;

# 创建学生表
CREATE TABLE student (
    num VARCHAR(20) PRIMARY KEY,
    name VARCHAR(20) NOT NULL,
    gender VARCHAR(10) NOT NULL,
    birthday DATE,
    class VARCHAR(20)
);

# 创建教师表
CREATE TABLE teacher (
    num VARCHAR(20) PRIMARY KEY,
    name VARCHAR(20) NOT NULL,
    gender VARCHAR(10) NOT NULL,
    birthday DATE,
    profession VARCHAR(20) NOT NULL,
    department VARCHAR(20) NOT NULL
);

# 创建课程表
CREATE TABLE course (
    num VARCHAR(20) PRIMARY KEY,
    name VARCHAR(20) NOT NULL,
    t_num VARCHAR(20) NOT NULL,
    FOREIGN KEY(t_num) REFERENCES teacher(num) 
);

# 成绩表
CREATE TABLE score (
    s_num VARCHAR(20) NOT NULL,
    c_num VARCHAR(20) NOT NULL, 
    score DECIMAL,
    FOREIGN KEY(s_num) REFERENCES student(num),	
    FOREIGN KEY(c_num) REFERENCES course(num),
    PRIMARY KEY(s_num, c_num)  # 这里设置联合primary key的原因是学生的num和课程的num只能有一个是相同的，因为同一个学生不会选两个一样的课
);

# 查看所有表
SHOW TABLES;

# 添加学生表数据
INSERT INTO student VALUES('101', '曾华', '男', '1977-09-01', '95033');
INSERT INTO student VALUES('102', '匡明', '男', '1975-10-02', '95031');
INSERT INTO student VALUES('103', '王丽', '女', '1976-01-23', '95033');
INSERT INTO student VALUES('104', '李军', '男', '1976-02-20', '95033');
INSERT INTO student VALUES('105', '王芳', '女', '1975-02-10', '95031');

# 添加教师表数据
INSERT INTO teacher VALUES('804', '李诚', '男', '1958-12-02', '副教授', '计算机系');
INSERT INTO teacher VALUES('856', '张旭', '男', '1969-03-12', '讲师', '电子工程系');
INSERT INTO teacher VALUES('825', '王萍', '女', '1972-05-05', '助教', '计算机系');

# 添加课程表数据
INSERT INTO course VALUES('3-105', '计算机导论', '825');
INSERT INTO course VALUES('3-245', '操作系统', '804');
INSERT INTO course VALUES('6-166', '数字电路', '856');

# 添加添加成绩表数据
INSERT INTO score VALUES('103', '3-105', '92');
INSERT INTO score VALUES('103', '3-245', '86');
INSERT INTO score VALUES('103', '6-166', '85');
INSERT INTO score VALUES('105', '3-105', '88');
INSERT INTO score VALUES('105', '3-245', '75');
INSERT INTO score VALUES('105', '6-166', '79');


# 查看表结构
SELECT * FROM course;
SELECT * FROM score;
SELECT * FROM student;
SELECT * FROM teacher;

结果：

mysql> SELECT * FROM course;
+-------+------------+-------+
| num   | name       | t_num |
+-------+------------+-------+
| 3-105 | 计算机导论 | 825   |
| 3-245 | 操作系统   | 804   |
| 6-166 | 数字电路   | 856   |
+-------+------------+-------+

mysql> SELECT * FROM score;
+-------+-------+-------+
| s_num | c_num | score |
+-------+-------+-------+
| 103   | 3-105 |    92 |
| 103   | 3-245 |    86 |
| 103   | 6-166 |    85 |
| 105   | 3-105 |    88 |
| 105   | 3-245 |    75 |
| 105   | 6-166 |    79 |
+-------+-------+-------+

mysql> SELECT * FROM student;
+-----+------+--------+------------+-------+
| num | name | gender | birthday   | class |
+-----+------+--------+------------+-------+
| 101 | 曾华 | 男     | 1977-09-01 | 95033 |
| 102 | 匡明 | 男     | 1975-10-02 | 95031 |
| 103 | 王丽 | 女     | 1976-01-23 | 95033 |
| 104 | 李军 | 男     | 1976-02-20 | 95033 |
| 105 | 王芳 | 女     | 1975-02-10 | 95031 |
+-----+------+--------+------------+-------+

mysql> SELECT * FROM teacher;
+-----+------+--------+------------+------------+------------+
| num | name | gender | birthday   | profession | department |
+-----+------+--------+------------+------------+------------+
| 804 | 李诚 | 男     | 1958-12-02 | 副教授     | 计算机系   |
| 825 | 王萍 | 女     | 1972-05-05 | 助教       | 计算机系   |
| 856 | 张旭 | 男     | 1969-03-12 | 讲师       | 电子工程系 |
+-----+------+--------+------------+------------+------------+

(2) 查表操作

mysql> select * from student;
+-----+------+--------+------------+-------+
| num | name | gender | birthday   | class |
+-----+------+--------+------------+-------+
| 101 | 曾华 | 男     | 1977-09-01 | 95033 |
| 102 | 匡明 | 男     | 1975-10-02 | 95031 |
| 103 | 王丽 | 女     | 1976-01-23 | 95033 |
| 104 | 李军 | 男     | 1976-02-20 | 95033 |
| 105 | 王芳 | 女     | 1975-02-10 | 95031 |
+-----+------+--------+------------+-------+

# 选取某些字段的行，注意了字段的顺序会决定最后表的呈现顺序
mysql> select name, gender, class from student;
+------+--------+-------+
| name | gender | class |
+------+--------+-------+
| 曾华 | 男     | 95033 |
| 匡明 | 男     | 95031 |
| 王丽 | 女     | 95033 |
| 李军 | 男     | 95033 |
| 王芳 | 女     | 95031 |
+------+--------+-------+

mysql> select distinct department from teacher;
+------------+
| department |
+------------+
| 计算机系   |
| 电子工程系 |
+------------+

mysql> select * from score where score between 60 and 80;
+-------+-------+-------+
| s_num | c_num | score |
+-------+-------+-------+
| 105   | 3-245 |    75 |
| 105   | 6-166 |    79 |
+-------+-------+-------+

# 注意要加括号哦
mysql> select * from score where score in (80, 86, 88);
+-------+-------+-------+
| s_num | c_num | score |
+-------+-------+-------+
| 103   | 3-245 |    86 |
| 105   | 3-105 |    88 |
+-------+-------+-------+

mysql> select * from student order by class desc;
+-----+------+--------+------------+-------+
| num | name | gender | birthday   | class |
+-----+------+--------+------------+-------+
| 101 | 曾华 | 男     | 1977-09-01 | 95033 |
| 103 | 王丽 | 女     | 1976-01-23 | 95033 |
| 104 | 李军 | 男     | 1976-02-20 | 95033 |
| 102 | 匡明 | 男     | 1975-10-02 | 95031 |
| 105 | 王芳 | 女     | 1975-02-10 | 95031 |
+-----+------+--------+------------+-------+

mysql> select * from score order by c_num asc, score desc;
+-------+-------+-------+
| s_num | c_num | score |
+-------+-------+-------+
| 103   | 3-105 |    92 |
| 105   | 3-105 |    88 |
| 103   | 3-245 |    86 |
| 105   | 3-245 |    75 |
| 103   | 6-166 |    85 |
| 105   | 6-166 |    79 |
+-------+-------+-------+

mysql> select count(*) from student where class='95031';
+----------+
| count(*) |
+----------+
|        2 |
+----------+

mysql> select s_num, c_num from score where score=(select max(score) from score);
+-------+-------+
| s_num | c_num |
+-------+-------+
| 103   | 3-105 |
+-------+-------+

或者：

mysql> select s_num, c_num from score order by score desc limit 0,1;
+-------+-------+
| s_num | c_num |
+-------+-------+
| 103   | 3-105 |
+-------+-------+

mysql> select c_num, avg(score) from score group by c_num;
+-------+------------+
| c_num | avg(score) |
+-------+------------+
| 3-105 |    90.0000 |
| 3-245 |    80.5000 |
| 6-166 |    82.0000 |
+-------+------------+

mysql> select c_num, avg(score), count(*) from score group by c_num having count(c_num)>=2 and c_num like '3%';
+-------+------------+----------+
| c_num | avg(score) | count(*) |
+-------+------------+----------+
| 3-105 |    90.0000 |        2 |
| 3-245 |    80.5000 |        2 |
+-------+------------+----------+

mysql> select name, c_num, score from student, score where student.num=score.s_num;
+------+-------+-------+
| name | c_num | score |
+------+-------+-------+
| 王丽 | 3-105 |    92 |
| 王丽 | 3-245 |    86 |
| 王丽 | 6-166 |    85 |
| 王芳 | 3-105 |    88 |
| 王芳 | 3-245 |    75 |
| 王芳 | 6-166 |    79 |
+------+-------+-------+

mysql> select c_num, avg(score) from score where s_num in (select num from student where class = '95031')
    -> group by c_num;
+-------+------------+
| c_num | avg(score) |
+-------+------------+
| 3-105 |    88.0000 |
| 3-245 |    75.0000 |
| 6-166 |    79.0000 |
+-------+------------+

mysql> select c_num, avg(score), count(*) from score group by c_num having count(c_num)>=2 and c_num like '3%';
+-------+------------+----------+
| c_num | avg(score) | count(*) |
+-------+------------+----------+
| 3-105 |    90.0000 |        2 |
| 3-245 |    80.5000 |        2 |
+-------+------------+----------+

mysql> select name, c_num, score from student, score where student.num=score.s_num;
+------+-------+-------+
| name | c_num | score |
+------+-------+-------+
| 王丽 | 3-105 |    92 |
| 王丽 | 3-245 |    86 |
| 王丽 | 6-166 |    85 |
| 王芳 | 3-105 |    88 |
| 王芳 | 3-245 |    75 |
| 王芳 | 6-166 |    79 |
+------+-------+-------+

mysql> select num, name,birthday from student where year(birthday)
    -> in (select year(birthday) from student where num in  (101, 108));
+-----+------+------------+
| num | name | birthday   |
+-----+------+------------+
| 101 | 曾华 | 1977-09-01 |
+-----+------+------------+

--------------to be continued--------------------2020.5.20