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Zero-based learning MySQL

Zero-based learning MySQL

solution

file, database

In order to solve the above problems, use a database that is more conducive to managing data, and it can manage data more effectively.

Take a life-like case to illustrate: If the library is to store books, then the database is to store data.

MySQL database installation and configuration

mysql5.5 mysql5.6 mysqI5.7 (stable) mysql8 higher version

Use the command line window to connect to the MYSQL database

mysql -h hostname -P port -u username -p password
Before logging in, make sure the service starts

net stop mysql服务名

net start mysql服务名

Operation Diagram

Navicat

Introduction: Graphical MySQL management software

SQLyog

Three-tier database structure

The so-called installation of the Mysql database is to install a database management system (DBMS) on the host computer. This management program can manage multiple databases. DBMS (database management system).
Multiple tables can be created in a database to store data (information).
The relationship between database management system (DBMS), database and table is shown in the figure; schematic diagram.

How data is stored in the database

Classification of SQL statements

DDL: data definition statement [create table, library...]

DML: data manipulation statement [add insert, modify update, delete delete]

DQL: data query statement [select]

DCL: data control statement [management database: such as user permission grant revoke]

create database

CHARACTER SET: Specifies the character set used by the database, if no character set is specified, the default is utf8
COLLATE: Specify the collation rules of the database character set (commonly used utf8 bin[case-sensitive]
utf8_general_ci[case-insensitive] Note that the default is utf8 general_ci)

# 演示数据库的操作
#创建一个名称为db01的数据库。[图形化和指令 演示]

#使用指令创建数据库
CREATE DATABASE db01;
#删除数据库指令
DROP DATABASE db01
#创建一个使用utf8字符集的hsp_db02数据库
CREATE DATABASE db02 CHARACTER SET utf8
#创建一个使用utf8字符集，并带校对规则的hsp_db03数据库
CREATE DATABASE db03 CHARACTER SET utf8 COLLATE utf8_bin
#校对规则 utf8_bin 区分大小 默认utf8_general_ci 不区分大小写

#下面是一条查询的sql , select 查询 * 表示所有字段 FROM 从哪个表
#WHERE 从哪个字段 NAME = 'tom' 查询名字是tom
SELECT *  
	FROM t1 
	WHERE NAME = 'tom'

View, delete database

Show database statements:

SHOW DATABASES

Show database creation statement:

SHOW CREATE DATABASE db_name

Database delete statement [must be used with caution]:

DROP DATABASE [IF EXISTS] db_ name

#演示删除和查询数据库
#查看当前数据库服务器中的所有数据库
SHOW DATABASES
#查看前面创建的hsp_db01数据库的定义信息
SHOW CREATE DATABASE `hsp_db01`
#在创建数据库,表的时候，为了规避关键字，可以使用反引号解决，比如有数据库的名称就叫做CREATE，那么就需要使用` `解决。

#删除前面创建的hsp_db01数据库
DROP DATABASE hsp_db01

backup restore database

Backup database (note: execute in DOS) command line

mysqldump -u 用户名 -p -B 数据库1 数据库2 数据库n >文件名.sql

Restore the database (note: enter the Mysql command line and execute again)

Source 文件名.sql

#练习 : database03.sql 备份db02 和 db03 库中的数据，并恢复

#备份, 要在Dos下执行mysqldump指令其实在mysql安装目录\bin
#这个备份的文件，就是对应的sql语句
mysqldump -u root -p -B db02 db03 > d:\\bak.sql

DROP DATABASE ecshop;

#恢复数据库(注意：进入Mysql命令行再执行)
source d:\\bak.sql
#第二个恢复方法， 直接将bak.sql的内容放到查询编辑器中，执行，相当于重新执行了一遍

Backup and restore database tables

Tables in the backup library

mysqldump -u 用户名 -p密码 数据库 表1 表2 表n > d:\\文件名.sql

create table

CREATE TABLE table_name
(
	field1 datatype,
    field2 datatype,
    field3 datatype
)character set 字符集 collate 校对规则 engine 存储引擎

field: specify the column name datatype: specify the column type (field type)
character set: If not specified, it is the character set of the database
collate: If not specified, it will be the collation rules of the database where it is located
engine: engine (this involves more content)

#指令创建表
#注意：db02创建表时，要根据需保存的数据创建相应的列，并根据数据的类型定义相应的列类型。例：user表 (快速入门案例 create_tab01.sql)
#id        	整形               [图形化，指令]                
#name 		字符串
#password 	字符串
#birthday 	日期
CREATE TABLE `user` (
	id INT, 
	`name` VARCHAR(255),
	`password` VARCHAR(255), 
	`birthday` DATE)
	CHARACTER SET utf8 COLLATE utf8_bin ENGINE INNODB;

Mysql common data types (column types)

Basic use of numeric (integer)

#演示整型的是一个
#使用tinyint 来演示范围 有符号 -128 ~ 127  如果没有符号 0-255
#说明： 表的字符集，校验规则, 存储引擎，老师使用默认
#1. 如果没有指定 unsinged , 则TINYINT就是有符号
#2. 如果指定 unsinged , 则TINYINT就是无符号 0-255
CREATE TABLE t3 (
	id TINYINT);
CREATE TABLE t4 (
	id TINYINT UNSIGNED);
	
INSERT INTO t3 VALUES(127); #这是非常简单的添加语句
SELECT * FROM t3

INSERT INTO t4 VALUES(255);
SELECT * FROM t4;

define an unsigned integer

create table t10 (id tinyint );//默认是有符号的
create table t11 (id tinyint unsigned);//无符号的 （后加unsigned就行）

Use of numeric type (bit)

1. Basic use

mysql > create table t05 (num bit(8));
mysql > insert into t05 (1, 3);
mysql > insert into t05 values(2, 65);

2. Details bit.sql

When the bit field is displayed, it is displayed in the form of bits.
You can still use the added value when querying
If a value is only 0, 1, you can consider using bit(1), which can save space
bit type. M specifies the number of digits, the default value is 1, and the range is 1-64

#演示bit类型使用
#说明
#1. bit(m) m 在 1-64
#2. 添加数据 范围 按照你给的位数来确定，比如 m = 8 表示一个字节 0~255
#3. 显示按照bit 
#4. 查询时，仍然可以按照数来查询
CREATE TABLE t05 (num BIT(8));
INSERT INTO t05 VALUES(255); # 按位显示 255 就是全1 （b'11111111'）
SELECT * FROM t05;
SELECT * FROM t05 WHERE num = 1;

Basic use of numeric (decimal)

FLOAT/DOUBLE [UNSIGNED]

Float single precision, Double double precision.
DECIMAL[M,D] [UNSIGNED]

More precise decimal places can be supported. M is the total number of decimal places (precision), and D is the number of digits after the decimal point (scale).
If D is 0, the value has no decimal point or fractional part. M max 65. D max is 30. If D is omitted, it defaults to 0. If M is omitted, the default is 10.
Suggestion: If you want the precision of decimals to be high, it is recommended to use decimal

#演示decimal类型、float、double使用

#创建表
CREATE TABLE t06 (
	num1 FLOAT,
	num2 DOUBLE,
	num3 DECIMAL(30,20));
#添加数据
INSERT INTO t06 VALUES(88.12345678912345, 88.12345678912345,88.12345678912345);
SELECT * FROM t06;

#decimal可以存放很大的数
CREATE TABLE t07 (
	num DECIMAL(65));
INSERT INTO t07 VALUES(8999999933338388388383838838383009338388383838383838383);

SELECT * FROM t07;
CREATE TABLE t08(
	num BIGINT UNSIGNED)
INSERT INTO t08 VALUES(8999999933338388388383838838383009338388383838383838383);
SELECT * FROM t08;

Basic use of strings

CHAR(size)

Fixed length string up to 255 characters

VARCHAR(size)0~65535

Variable length character string up to 65532 bytes [utf8 encoding up to 21844 characters ((65535-3) / 3) of which 1-3 bytes are used for record size]

#演示字符串类型使用char varchar
#注释的快捷键 shift+ctrl+c , 注销注释 shift+ctrl+r
-- CHAR(size)
-- 固定长度字符串 最大255 字符 
-- VARCHAR(size)    0~65535字节
-- 可变长度字符串 最大65532字节  【utf8编码最大21844字符 1-3个字节用于记录大小】
-- 如果表的编码是 utf8 varchar(size) size = (65535-3) / 3 = 21844
-- 如果表的编码是 gbk varchar(size) size = (65535-3) / 2 = 32766
CREATE TABLE t09 (
	`name` CHAR(255));

CREATE TABLE t10 (
	`name` VARCHAR(32766)) CHARSET gbk;

DROP TABLE t10;

String Usage Details

1. Details 1

char(4) //This 4 represents the number of characters (maximum 255), not the number of bytes. Whether it is Chinese or letters, it is four, and it is calculated by character.
varchar(4) //This 4 represents the number of characters, whether it is letters or Chinese, the data is stored in the code of the defined table
Whether it is Chinese or English letters, there are up to 4 stored, which are stored according to characters.

2. Details 2

char(4) is a fixed length (fixed size), that is to say, even if you insert 'aa', it will occupy the allocated space of 4 characters.
Varchar(4) is variable length (changing size), that is to say, if you insert 'aa', the actual occupied space is not 4 characters, but allocated according to the actual occupied space (Note: varchar itself still needs to occupy 1-3 bytes to record the storage content length)L(实际数据大小)+(1-3)字节

3. Details 3

When to use char and when to use varchar

If the data is of fixed length, it is recommended to use char, such as md5 password, zip code, mobile phone number, ID number, etc. char(32)
If the length of a field is uncertain, we use varchar, such as messages, articles
Query speed: char > varchar

4. Details 4

When storing text, you can also use the Text data type. TEXT column can be regarded as VARCHAR column, note that Text cannot have a default value. Size 0-2^16 bytes. If you want to store more characters, you can choose
MEDIUMTEXT 0O-2^24 or LONGTEXT 0~2^32

#演示字符串类型的使用细节
#char(4) 和 varchar(4) 这个4表示的是字符，而不是字节, 不区分字符是汉字还是字母
CREATE TABLE t11(
	`name` CHAR(4));
INSERT INTO t11 VALUES('你好你好');

SELECT * FROM t11;

CREATE TABLE t12(
	`name` VARCHAR(4));
INSERT INTO t12 VALUES('你好你好');
INSERT INTO t12 VALUES('ab北京');
SELECT * FROM t12;

#如果varchar 不够用，可以考试使用mediumtext 或者longtext, 
#如果想简单点，可以使用直接使用text
CREATE TABLE t13( content TEXT, content2 MEDIUMTEXT , content3 LONGTEXT);
INSERT INTO t13 VALUES('你好你教育', '你好你教育100', '你好你教育1000~~');
SELECT * FROM t13;

Basic use of date types

CREATE TABLE birthday6( t1 DATE, t2 DATETIME,
t3 TIMESTAMP NOT NULL DEFAULTCURRENT TIMESTAMP ON UPDATE
CURRENT TIMESTAMP ); timestamp时间戳
# NOT NULL DEFAULTCURRENT TIMESTAMP ON UPDATE CURRENT TIMESTAMP 意思是没有默认值的话会根据当前时间自动更新

mysql> INSERT INTO birthday (t1,t2)
VALUES('2022-11-11',2022-11-11 10:10:10');

Details of the date type

TimeStamp is automatically updated during Insert and update.

#演示时间相关的类型
#创建一张表, date , datetime , timestamp
CREATE TABLE t14 (
	birthday DATE , -- 生日
	job_time DATETIME, -- 记录年月日 时分秒
	login_time TIMESTAMP 
		NOT NULL DEFAULT CURRENT_TIMESTAMP 
		ON UPDATE CURRENT_TIMESTAMP); -- 登录时间, 如果希望login_time列自动更新, 需要配置
		
SELECT * FROM t14;
INSERT INTO t14(birthday, job_time) 
	VALUES('2022-11-11','2022-11-11 10:10:10');
-- 如果我们更新 t14 表的某条记录，login_time列会自动的以当前时间进行更新

Create table exercise

#创建表的课堂练习
-- 字段	属性
-- Id	整形
-- name	字符型
-- sex	字符型
-- brithday	日期型（date）
-- entry_date	日期型   (date)
-- job	字符型
-- Salary	小数型
-- resume	文本型
-- 自己一定要练习一把
CREATE TABLE `emp` (
	id INT,
	`name` VARCHAR(32),
	sex CHAR(1), 
	brithday DATE,
	entry_date DATETIME,
	job VARCHAR(32),
	salary DOUBLE,
	`resume` TEXT) CHARSET utf8 COLLATE utf8_bin ENGINE INNODB;
-- 添加一条
INSERT INTO `emp`
	VALUES(100, '小妖怪', '男', '2000-11-11', 
		'2010-11-10 11:11:11', '巡山的', 3000, '大王叫我来巡山');
		
SELECT * FROM `emp`;

Modify Table - Basic Introduction

Modification Sheet - Class Exercise

NOT NULL DEFAULT ''Empty NULL is not allowed, and the default is an empty ' ' character.

#修改表的操作练习
--  员工表emp的上增加一个image列，varchar类型(要求在resume后面)。
ALTER TABLE emp 
	ADD image VARCHAR(32) NOT NULL DEFAULT '' 
	AFTER RESUME
DESC employee -- 显示表结构，可以查看表的所有列
--  修改job列，使其长度为60。
ALTER TABLE emp
	MODIFY job VARCHAR(60) NOT NULL DEFAULT ''
--  删除sex列。
ALTER TABLE emp
	DROP sex
--  表名改为employee。
RENAME TABLE emp TO employee
--  修改表的字符集为utf8 
ALTER TABLE employee CHARACTER SET utf8
--  列名name修改为us	er_name
ALTER TABLE employee 
	CHANGE `name` `user_name` VARCHAR(64) NOT NULL DEFAULT ''
DESC employee

Database C[create]R[read]U[update]D[delete] statement

Insert statement (add data)
Update statement (update data)
Delete statement (delete data)
Select statement (find data)

Insert statement

Insert data into a table using the INSERT statement.

#练习insert 语句
-- 创建一张商品表goods (id  int , goods_name varchar(10), price double );
-- 添加2条记录
CREATE TABLE `goods` (
	id INT ,
	goods_name VARCHAR(10), -- 长度10
	price DOUBLE NOT NULL DEFAULT 100 );
-- 添加数据
INSERT INTO `goods` (id, goods_name, price) 
	VALUES(10, '华为手机', 2000);
INSERT INTO `goods` (id, goods_name, price) 
	VALUES(20, '苹果手机', 3000);
SELECT * FROM goods;

CREATE TABLE `goods2` (
	id INT ,
	goods_name VARCHAR(10), -- 长度10
	price DOUBLE NOT NULL DEFAULT 100 );

Details

#说明insert 语句的细节
-- 1.插入的数据应与字段的数据类型相同。
--       比如 把 'abc' 添加到 int 类型会错误
INSERT INTO `goods` (id, goods_name, price) 
	VALUES('abc', '小米手机', 2000);
-- 2. 数据的长度应在列的规定范围内，例如：不能将一个长度为80的字符串加入到长度为40的列中。
INSERT INTO `goods` (id, goods_name, price) 
	VALUES(40, 'vovo手机vovo手机vovo手机vovo手机vovo手机', 3000);
-- 3. 在values中列出的数据位置必须与被加入的列的排列位置相对应。
INSERT INTO `goods` (id, goods_name, price)  -- 不对
	VALUES('vovo手机',40, 2000);
-- 4. 字符和日期型数据应包含在单引号中。
INSERT INTO `goods` (id, goods_name, price) 
	VALUES(40, vovo手机, 3000); -- 错误的 vovo手机 应该 'vovo手机'
-- 5. 列可以插入空值[前提是该字段允许为空（如果指定 not null 则不可以）]，insert into table value(null)
INSERT INTO `goods` (id, goods_name, price) 
	VALUES(40, 'vovo手机', NULL);
-- 6. insert into tab_name (列名..)  values (),(),()  形式添加多条记录
INSERT INTO `goods` (id, goods_name, price) 
	VALUES(50, '三星手机', 2300),(60, '海尔手机', 1800);
-- 7. 如果是给表中的所有字段添加数据，可以不写前面的字段名称
INSERT INTO `goods`   
	VALUES(70, 'IBM手机', 5000);
-- 8. 默认值的使用，当不给某个字段值时，如果有默认值就会添加默认值，否则报错
      -- 如果某个列 没有指定 not null ,那么当添加数据时，没有给定值，则会默认给null
      -- 如果我们希望指定某个列的默认值，可以在创建表时指定
INSERT INTO `goods` (id, goods_name)   
	VALUES(80, '格力手机');

SELECT * FROM goods;

INSERT INTO `goods2` (id, goods_name)   
	VALUES(10, '顺平手机');
SELECT * FROM goods2;

update statement

Use the update statement to modify the data in the table

basic use

-- 演示update语句
-- 要求: 在上面创建的employee表中修改表中的纪录
-- 1. 将所有员工薪水修改为5000元。[如果没有带where 条件，会修改所有的记录，因此要小心]
UPDATE employee SET salary = 5000 
-- 2. 将姓名为 小妖怪 的员工薪水修改为3000元。
UPDATE employee 
	SET salary = 3000 
	WHERE user_name = '小妖怪' 
-- 3. 将 老妖怪 的薪水在原有基础上增加1000元
INSERT INTO employee 
	VALUES(200, '老妖怪', '1990-11-11', '2000-11-11 10:10:10', '捶背的', 5000, '给大王捶背', 'd:\\a.jpg');

UPDATE employee 
	SET salary = salary + 1000 
	WHERE user_name = '老妖怪' 

-- 可以修改多个列的值
UPDATE employee 
	SET salary = salary + 1000 , job = '出主意的'
	WHERE user_name = '老妖怪' 
SELECT * FROM employee;

usage details

The WHERE clause specifies which rows should be updated. If there is no WHERE clause, all rows (records) are updated.
If you need to modify multiple fields, you can passset 字段1=值1,字段2=值2...

delete statement

Use the delete statement to delete data in the table

Delete can only be deleted by row, not by column.

-- delete 语句演示

--  删除表中名称为’老妖怪’的记录。
DELETE FROM employee 
	WHERE user_name = '老妖怪';
--  删除表中所有记录, 老师提醒，一定要小心
DELETE FROM employee;

-- Delete语句不能删除某一列的值（可使用update 设为 null 或者 ''）
UPDATE employee SET job = '' WHERE user_name = '老妖怪';

SELECT * FROM employee

-- 要删除这个表
DROP TABLE employee;

usage details

If no where clause is used, all data in the table will be deleted.
The Delete statement cannot delete the value of a column (you can use update to set it to null or "")
Use the delete statement to delete records without deleting the table itself. To drop a table, use the droptable statement. drop table 表名;

select statement

basic grammar

Notes (create test table student table)

Select specifies which columns of data to query.
column specifies the column name.
The * means to query all columns.
From specifies which table to query.
DISTINCT is optional, indicating whether to remove duplicate data when displaying results.

practise

-- select 语句【重点 难点】
CREATE TABLE student(
	id INT NOT NULL DEFAULT 1,
	NAME VARCHAR(20) NOT NULL DEFAULT '',
	chinese FLOAT NOT NULL DEFAULT 0.0,
	english FLOAT NOT NULL DEFAULT 0.0,
	math FLOAT NOT NULL DEFAULT 0.0
);

INSERT INTO student(id,NAME,chinese,english,math) VALUES(1,'韩顺平',89,78,90);
INSERT INTO student(id,NAME,chinese,english,math) VALUES(2,'张飞',67,98,56);
INSERT INTO student(id,NAME,chinese,english,math) VALUES(3,'宋江',87,78,77);
INSERT INTO student(id,NAME,chinese,english,math) VALUES(4,'关羽',88,98,90);
INSERT INTO student(id,NAME,chinese,english,math) VALUES(5,'赵云',82,84,67);
INSERT INTO student(id,NAME,chinese,english,math) VALUES(6,'欧阳锋',55,85,45);
INSERT INTO student(id,NAME,chinese,english,math) VALUES(7,'黄蓉',75,65,30);
INSERT INTO student(id,NAME,chinese,english,math) VALUES(8,'韩信',45,65,99);

SELECT * FROM student;

-- 查询表中所有学生的信息。
SELECT * FROM student;
-- 查询表中所有学生的姓名和对应的英语成绩。
SELECT `name`,english FROM student;
-- 过滤表中重复数据 distinct 。
SELECT DISTINCT english FROM student;
-- 要查询的记录，每个字段都相同，才会去重
SELECT DISTINCT `name`, english FROM student;

Use expressions to operate on the columns of the query

The as statement can be used in the select statement

practise

-- select 语句的使用

-- 统计每个学生的总分
SELECT `name`, (chinese+english+math) FROM student;
-- 在所有学生总分加10分的情况
SELECT `name`, (chinese + english + math + 10) FROM student;
-- 使用别名表示学生分数。
SELECT `name` AS '名字', (chinese + english + math + 10) AS total_score 
	FROM student;

Operators frequently used in where clauses

Among them, BETWEEN ... AND is a closed interval.

Use where clause to filter queries

_: match any character;
%: Match 0 or more characters;
[ ]: Match any character in [ ] (if the characters to be compared are continuous, you can use a hyphen "-" to express);
[^ ]: Does not match any character in [ ].

-- select 语句
-- 查询姓名为赵云的学生成绩
SELECT * FROM student 
	WHERE `name` = '赵云'
-- 查询英语成绩大于90分的同学
SELECT * FROM student 
	WHERE english > 90
-- 查询总分大于200分的所有同学

SELECT * FROM student 
	WHERE (chinese + english + math) > 200
	
-- 查询math大于60 并且(and) id大于4的学生成绩
SELECT * FROM student
	WHERE math >60 AND id > 4
-- 查询英语成绩大于语文成绩的同学
SELECT * FROM student
	WHERE english > chinese
-- 查询总分大于200分 并且 数学成绩小于语文成绩,的姓赵的学生.
-- 赵% 表示 名字以赵开头的就可以
SELECT * FROM student
	WHERE (chinese + english + math) > 200 AND 
		math < chinese AND `name` LIKE '赵%'
-- 查询英语分数在 80－90之间的同学。
SELECT * FROM student
	WHERE english >= 80 AND english <= 90;
SELECT * FROM student
	WHERE english BETWEEN 80 AND 90; -- between .. and .. 是 闭区间
-- 查询数学分数为89,90,91的同学。
SELECT * FROM student 
	WHERE math = 89 OR math = 90 OR math = 91;
SELECT * FROM student 
	WHERE math IN (89, 90, 91);
-- 查询所有姓李的学生成绩。
SELECT * FROM student 
	WHERE `name` LIKE '韩%'
-- 查询数学分>80，语文分>80的同学

Use the order by clause to sort query results

Order by specifies the column to be sorted. The column to be sorted can be the column name in the table or the
column name specified after the select statement.
Asc ascending order [default], Desc descending order
The ORDER BY clause should be at the end of the SELECT statement.

-- 演示order by使用
-- 对数学成绩排序后输出【升序】。
SELECT * FROM student 
	ORDER BY math;
-- 对总分按从高到低的顺序输出 [降序] -- 使用别名排序
SELECT `name` , (chinese + english + math) AS total_score FROM student 
	ORDER BY total_score DESC;
-- 对姓韩的学生成绩[总分]排序输出(升序) where + order by
SELECT `name`, (chinese + english + math) AS total_score FROM student
	WHERE `name` LIKE '韩%'
	ORDER BY total_score;

Aggregation/statistical functions

count

-- 演示mysql的统计函数的使用
-- 统计一个班级共有多少学生？
SELECT COUNT(*) FROM student;
-- 统计数学成绩大于90的学生有多少个？
SELECT COUNT(*) FROM student
	WHERE math > 90
-- 统计总分大于250的人数有多少？
SELECT COUNT(*) FROM student
	WHERE (math + english + chinese) > 250
-- count(*) 和 count(列) 的区别 
-- 解释 :count(*) 返回满足条件的记录的行数
-- count(列): 统计满足条件的某列有多少个，但是会排除 为null的情况
CREATE TABLE t15 (
	`name` VARCHAR(20));
INSERT INTO t15 VALUES('tom');
INSERT INTO t15 VALUES('jack');
INSERT INTO t15 VALUES('mary');
INSERT INTO t15 VALUES(NULL);
SELECT * FROM t15;

SELECT COUNT(*) FROM t15; -- 4
SELECT COUNT(`name`) FROM t15;-- 3


-- 演示sum函数的使用
-- 统计一个班级数学总成绩？
SELECT SUM(math) FROM student;
-- 统计一个班级语文、英语、数学各科的总成绩
SELECT SUM(math) AS math_total_score,SUM(english),SUM(chinese) FROM student;
-- 统计一个班级语文、英语、数学的成绩总和
SELECT SUM(math + english + chinese) FROM student;
-- 统计一个班级语文成绩平均分
SELECT SUM(chinese)/ COUNT(*)  FROM student;
SELECT SUM(`name`) FROM student;

-- 演示avg的使用
-- 练习：
-- 求一个班级数学平均分？
SELECT AVG(math) FROM student;
-- 求一个班级总分平均分
SELECT AVG(math + english + chinese) FROM student;

-- 演示max 和 min的使用
-- 求班级最高分和最低分（数值范围在统计中特别有用）
SELECT MAX(math + english + chinese), MIN(math + english + chinese) 
	FROM student;

-- 求出班级数学最高分和最低分
SELECT MAX(math) AS math_high_socre, MIN(math)  AS math_low_socre
	FROM student;

sum

The Sum function returns the sum of rows that meet the where condition and is generally used in numeric columns.

avg

The AVG function returns the average value of a column that satisfies the where condition

max/min

The Max/min function returns the maximum/minimum value of a column that satisfies the where condition

Group columns using the group by clause

Use the having clause to filter the grouped results

group by is used to group and count query results, (schematic diagram)

The having clause is used to limit the grouped display results

CREATE TABLE dept( /*部门表*/
deptno MEDIUMINT   UNSIGNED  NOT NULL  DEFAULT 0, 
dname VARCHAR(20)  NOT NULL  DEFAULT "",
loc VARCHAR(13) NOT NULL DEFAULT ""
);

INSERT INTO dept VALUES(10, 'ACCOUNTING', 'NEW YORK'), 
(20, 'RESEARCH', 'DALLAS'), 
(30, 'SALES', 'CHICAGO'), 
(40, 'OPERATIONS', 'BOSTON');

SELECT * FROM dept;

-- 员工表

CREATE TABLE emp
(empno  MEDIUMINT UNSIGNED  NOT NULL  DEFAULT 0, /*编号*/
ename VARCHAR(20) NOT NULL DEFAULT "", /*名字*/
job VARCHAR(9) NOT NULL DEFAULT "",/*工作*/
mgr MEDIUMINT UNSIGNED ,/*上级编号*/
hiredate DATE NOT NULL,/*入职时间*/
sal DECIMAL(7,2)  NOT NULL,/*薪水*/
comm DECIMAL(7,2) ,/*红利 奖金*/
deptno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0 /*部门编号*/
);

-- 添加测试数据
 INSERT INTO emp VALUES(7369, 'SMITH', 'CLERK', 7902, '1990-12-17', 800.00,NULL , 20), 
(7499, 'ALLEN', 'SALESMAN', 7698, '1991-2-20', 1600.00, 300.00, 30),  
(7521, 'WARD', 'SALESMAN', 7698, '1991-2-22', 1250.00, 500.00, 30),  
(7566, 'JONES', 'MANAGER', 7839, '1991-4-2', 2975.00,NULL,20),  
(7654, 'MARTIN', 'SALESMAN', 7698, '1991-9-28',1250.00,1400.00,30),  
(7698, 'BLAKE','MANAGER', 7839,'1991-5-1', 2850.00,NULL,30),  
(7782, 'CLARK','MANAGER', 7839, '1991-6-9',2450.00,NULL,10),  
(7788, 'SCOTT','ANALYST',7566, '1997-4-19',3000.00,NULL,20),  
(7839, 'KING','PRESIDENT',NULL,'1991-11-17',5000.00,NULL,10),  
(7844, 'TURNER', 'SALESMAN',7698, '1991-9-8', 1500.00, NULL,30),  
(7900, 'JAMES','CLERK',7698, '1991-12-3',950.00,NULL,30),  
(7902, 'FORD', 'ANALYST',7566,'1991-12-3',3000.00, NULL,20),  
(7934,'MILLER','CLERK',7782,'1992-1-23', 1300.00, NULL,10);

SELECT * FROM emp;

-- 工资级别
#工资级别表
CREATE TABLE salgrade
(
grade MEDIUMINT UNSIGNED NOT NULL DEFAULT 0, /*工资级别*/ 
losal DECIMAL(17,2)  NOT NULL, /* 该级别的最低工资 */
hisal DECIMAL(17,2)  NOT NULL /* 该级别的最高工资*/
);

INSERT INTO salgrade VALUES (1,700,1200);
INSERT INTO salgrade VALUES (2,1201,1400);
INSERT INTO salgrade VALUES (3,1401,2000);
INSERT INTO salgrade VALUES (4,2001,3000);
INSERT INTO salgrade VALUES (5,3001,9999);

SELECT * FROM salgrade;
SELECT * FROM dept;
SELECT * FROM emp;

# 演示group by + having
GROUP by用于对查询的结果分组统计, (示意图)
-- having子句用于限制分组显示结果.
-- ?如何显示每个部门的平均工资和最高工资
-- 老韩分析: avg(sal) max(sal)
-- 按照部分来分组查询
SELECT AVG(sal), MAX(sal) , deptno 
	FROM  emp GROUP BY deptno; 
-- 使用数学方法，对小数点进行处理
SELECT FORMAT(AVG(sal),2), MAX(sal) , deptno 
	FROM  emp GROUP BY deptno; 

-- ?显示每个部门的每种岗位的平均工资和最低工资
-- 老师分析 1. 显示每个部门的平均工资和最低工资
--          2. 显示每个部门的每种岗位的平均工资和最低工资
SELECT AVG(sal), MIN(sal) , deptno, job 
	FROM  emp GROUP BY deptno, job; 

-- ?显示平均工资低于2000的部门号和它的平均工资 // 别名

-- 老师分析 [写sql语句的思路是化繁为简,各个击破]
-- 1. 显示各个部门的平均工资和部门号
-- 2. 在1的结果基础上，进行过滤，保留 AVG(sal) < 2000
-- 3. 使用别名进行过滤 

SELECT AVG(sal), deptno 
	FROM emp GROUP BY deptno
		HAVING AVG(sal) < 2000;
-- 使用别名		
SELECT AVG(sal) AS avg_sal, deptno 
	FROM emp GROUP BY deptno
		HAVING avg_sal < 2000;

String related functions

-- 演示字符串相关函数的使用  ， 使用emp表来演示
-- CHARSET(str)	返回字串字符集
SELECT CHARSET(ename) FROM emp;
-- CONCAT (string2  [,... ])	连接字串, 将多个列拼接成一列
SELECT CONCAT(ename, ' 工作是 ', job) FROM emp;

-- INSTR (string ,substring )	返回substring在string中出现的位置,没有返回0
-- dual 亚元表, 系统表 可以作为测试表使用
SELECT INSTR('hanshunping', 'ping') FROM DUAL; 

-- UCASE (string2 )	转换成大写
SELECT UCASE(ename) FROM emp;

-- LCASE (string2 )	转换成小写

SELECT LCASE(ename) FROM emp;
-- LEFT (string2 ,length )	从string2中的左边起取length个字符
-- RIGHT (string2 ,length )	从string2中的右边起取length个字符
SELECT LEFT(ename, 2) FROM emp;

-- LENGTH (string )	string长度[按照字节]
SELECT LENGTH(ename) FROM emp;
-- REPLACE (str ,search_str ,replace_str ) 	
-- 在str中用 replace_str 替换 search_str
-- 如果是 manager 就替换成 经理
SELECT ename, REPLACE(job,'MANAGER', '经理')  FROM emp;

-- STRCMP (string1 ,string2 )	逐字符比较两字串大小
SELECT STRCMP('hsp', 'hsp') FROM DUAL;
-- SUBSTRING (str , position  [,length ])	
-- 从str的position开始【从1开始计算】,取length个字符
-- 从ename 列的第一个位置开始取出2个字符
SELECT SUBSTRING(ename, 1, 2) FROM emp;

-- LTRIM (string2 ) RTRIM (string2 )  TRIM(string)
-- 去除前端空格或后端空格
SELECT LTRIM('  韩顺平教育') FROM DUAL;
SELECT RTRIM('韩顺平教育   ') FROM DUAL;
SELECT TRIM('    韩顺平教育   ') FROM DUAL;

-- 练习: 以首字母小写的方式显示所有员工emp表的姓名
-- 方法1 
-- 思路先取出ename 的第一个字符，转成小写的
-- 把他和后面的字符串进行拼接输出即可

SELECT CONCAT(LCASE(SUBSTRING(ename,1,1)),  SUBSTRING(ename,2)) AS new_name
	FROM emp;  

SELECT CONCAT(LCASE(LEFT(ename,1)),  SUBSTRING(ename,2)) AS new_name
	FROM emp;

math related functions

rand()Returns a random floating point value v in the range 0 to 1 (ie, its range is 0<=v<=1.0). If an integer parameter N has been specified, it is used as the seed value used to generate the repeating sequence.

-- 演示数学相关函数

-- ABS(num)	绝对值
SELECT ABS(-10) FROM DUAL;
-- BIN (decimal_number )十进制转二进制
SELECT BIN(10) FROM DUAL;
-- CEILING (number2 )	向上取整, 得到比num2 大的最小整数
SELECT CEILING(-1.1) FROM DUAL;

-- CONV(number2,from_base,to_base)	进制转换
-- 下面的含义是 8 是十进制的8, 转成 2进制输出
SELECT CONV(8, 10, 2) FROM DUAL;
-- 下面的含义是 8 是16进制的8, 转成 2进制输出
SELECT CONV(16, 16, 10) FROM DUAL;

-- FLOOR (number2)	向下取整,得到比 num2 小的最大整数
SELECT FLOOR(-1.1) FROM DUAL;

-- FORMAT (number,decimal_places )	保留小数位数(四舍五入)
SELECT FORMAT(78.125458,2) FROM DUAL;

-- HEX (DecimalNumber )	转十六进制

-- LEAST (number , number2  [,..])	求最小值
SELECT LEAST(0,1, -10, 4) FROM DUAL;
-- MOD (numerator ,denominator )	求余
SELECT MOD(10, 3) FROM DUAL;

-- RAND([seed])	RAND([seed]) 返回随机数 其范围为 0 ≤ v ≤ 1.0
-- 1. 如果使用 rand() 每次返回不同的随机数 ，在 0 ≤ v ≤ 1.0
-- 2. 如果使用 rand(seed) 返回随机数, 范围 0 ≤ v ≤ 1.0, 如果seed不变，该随机数也不变了
SELECT RAND() FROM DUAL;

SELECT CURRENT_TIMESTAMP() FROM DUAL;

Date and time related functions

-- 日期时间相关函数

-- CURRENT_DATE (  )	当前日期
SELECT CURRENT_DATE() FROM DUAL;
-- CURRENT_TIME (  )	当前时间
SELECT CURRENT_TIME()  FROM DUAL;
-- CURRENT_TIMESTAMP (  ) 当前时间戳
SELECT CURRENT_TIMESTAMP()  FROM DUAL;

-- 创建测试表 信息表
CREATE TABLE mes(
	id INT , 
	content VARCHAR(30), 
	send_time DATETIME);
	
	
-- 添加一条记录
INSERT INTO mes 
	VALUES(1, '北京新闻', CURRENT_TIMESTAMP()); 
INSERT INTO mes VALUES(2, '上海新闻', NOW());
INSERT INTO mes VALUES(3, '广州新闻', NOW());

SELECT * FROM mes;
SELECT NOW() FROM DUAL;

-- 上应用实例
-- 显示所有新闻信息，发布日期只显示 日期，不用显示时间.
SELECT id, content, DATE(send_time) 
	FROM mes;
-- 请查询在10分钟内发布的新闻, 思路一定要梳理一下.
SELECT * 
	FROM mes
	WHERE DATE_ADD(send_time, INTERVAL 10 MINUTE) >= NOW()

SELECT * 
	FROM mes
	WHERE send_time >= DATE_SUB(NOW(), INTERVAL 10 MINUTE) 

-- 请在mysql 的sql语句中求出 2011-11-11 和 1990-1-1 相差多少天
SELECT DATEDIFF('2011-11-11', '1990-01-01') FROM DUAL;
-- 请用mysql 的sql语句求出你活了多少天? [练习] 1986-11-11 出生
SELECT DATEDIFF(NOW(), '1986-11-11') FROM DUAL;
-- 如果你能活80岁，求出你还能活多少天.[练习] 1986-11-11 出生
-- 先求出活80岁 时, 是什么日期 X
-- 然后在使用 datediff(x, now()); 1986-11-11->datetime
-- INTERVAL 80 YEAR ： YEAR 可以是 年月日，时分秒
-- '1986-11-11' 可以date,datetime timestamp 
SELECT DATEDIFF(DATE_ADD('1986-11-11', INTERVAL 80 YEAR), NOW()) 
	FROM DUAL;
	
SELECT TIMEDIFF('10:11:11', '06:10:10') FROM DUAL;

-- YEAR|Month|DAY|DATE (datetime)
SELECT YEAR(NOW()) FROM DUAL;
SELECT MONTH(NOW()) FROM DUAL;
SELECT DAY(NOW()) FROM DUAL;
SELECT MONTH('2013-11-10') FROM DUAL;
-- unix_timestamp() : 返回的是1970-1-1 到现在的秒数
SELECT UNIX_TIMESTAMP() FROM DUAL;
-- FROM_UNIXTIME() : 可以把一个unix_timestamp 秒数[时间戳]，转成指定格式的日期
-- %Y-%m-%d 格式是规定好的，表示年月日
-- 意义：在开发中，可以存放一个整数，然后表示时间，通过FROM_UNIXTIME转换
--   
SELECT FROM_UNIXTIME(1618483484, '%Y-%m-%d') FROM DUAL;
SELECT FROM_UNIXTIME(1618483100, '%Y-%m-%d %H:%i:%s') FROM DUAL;

SELECT * FROM mysql.user \G

Encryption and System Functions

-- 演示加密函数和系统函数

-- USER()	查询用户
-- 可以查看登录到mysql的有哪些用户，以及登录的IP
SELECT USER() FROM DUAL; -- 返回 用户@IP地址
-- DATABASE()	查询当前使用数据库名称
SELECT DATABASE();

-- MD5(str)	为字符串算出一个 MD5 32的字符串，常用(用户密码)加密
-- root 密码是 timerring -> 加密md5 -> 在数据库中存放的是加密后的密码
SELECT MD5('timerring') FROM DUAL;
SELECT LENGTH(MD5('timerring')) FROM DUAL;

-- 演示用户表，存放密码时，是md5
CREATE TABLE timerring_user
	(id INT , 
	`name` VARCHAR(32) NOT NULL DEFAULT '', 
	pwd CHAR(32) NOT NULL DEFAULT '');
INSERT INTO timerring_user 
	VALUES(100, '谈莫瑞', MD5('timerring'));
SELECT * FROM timerring_user;

SELECT * FROM timerring_user  -- SQL注入问题
	WHERE `name`='谈莫瑞' AND pwd = MD5('timerring')  


-- PASSWORD(str) -- 加密函数, MySQL数据库的用户密码就是 PASSWORD函数加密

SELECT PASSWORD('timerring') FROM DUAL; -- 数据库的 *81220D972A52D4C51BB1C37518A2613706220DAC


-- select * from mysql.user \G 	从原文密码str 计算并返回密码字符串
-- 通常用于对mysql数据库的用户密码加密
-- mysql.user 表示 数据库.表 
SELECT * FROM mysql.user

flow control function

# 演示流程控制语句

# IF(expr1,expr2,expr3)	如果expr1为True ,则返回 expr2 否则返回 expr3
SELECT IF(TRUE, '北京', '上海') FROM DUAL;
# IFNULL(expr1,expr2)	如果expr1不为空NULL,则返回expr1,否则返回expr2
SELECT IFNULL( NULL, '教育') FROM DUAL;
# SELECT CASE WHEN expr1 THEN expr2 WHEN expr3 THEN expr4 ELSE expr5 END; [类似多重分支.]
# 如果expr1 为TRUE,则返回expr2,如果expr2 为t, 返回 expr4, 否则返回 expr5

SELECT CASE 
	WHEN TRUE THEN 'jack'  -- jack
	WHEN FALSE THEN 'tom' 
	ELSE 'mary' END

-- 1. 查询emp 表, 如果 comm 是null , 则显示0.0
--    老师说明，判断是否为null 要使用 is null, 判断不为空 使用 is not
SELECT ename, IF(comm IS NULL , 0.0, comm)
	FROM emp;
SELECT ename, IFNULL(comm, 0.0)
	FROM emp;
-- 2. 如果emp 表的 job 是 CLERK 则显示 职员， 如果是 MANAGER 则显示经理
--     如果是 SALESMAN 则显示 销售人员，其它正常显示

SELECT ename, (SELECT CASE 
		WHEN job = 'CLERK' THEN '职员' 
		WHEN job = 'MANAGER' THEN '经理'
		WHEN job = 'SALESMAN' THEN '销售人员' 
		ELSE job END) AS 'job'
	FROM emp; 

SELECT * FROM emp;
SELECT * FROM dept;
SELECT * FROM salgrade;

mysql table query – enhanced

introduce

-- 查询加强
-- ■ 使用where子句
-- 	?如何查找1992.1.1后入职的员工
-- 老师说明： 在mysql中,日期类型可以直接比较, 需要注意格式
SELECT * FROM emp
	WHERE hiredate > '1992-01-01'
-- ■ 如何使用like操作符(模糊)
-- 	%: 表示0到多个任意字符 _: 表示单个任意字符
-- 	?如何显示首字符为S的员工姓名和工资
SELECT ename, sal FROM emp
	WHERE ename LIKE 'S%'
-- 	?如何显示第三个字符为大写O的所有员工的姓名和工资
SELECT ename, sal FROM emp
	WHERE ename LIKE '__O%'

-- ■ 如何显示没有上级的雇员的情况
SELECT * FROM emp
	WHERE mgr IS NULL;
-- ■ 查询表结构 
DESC emp 

-- 使用order by子句
--   ?如何按照工资的从低到高的顺序[升序]，显示雇员的信息
SELECT * FROM emp
	ORDER BY sal 
--   ?按照部门号升序而雇员的工资降序排列 , 显示雇员信息

SELECT * FROM emp
	ORDER BY deptno ASC , sal DESC;

Paging query

Basic syntax: select.... limit start, rows
means start+1fetching from the row, fetching rowsthe row, and startcounting from 0

-- 分页查询
-- 按雇员的id号升序取出， 每页显示3条记录，请分别显示 第1页，第2页，第3页

-- 第1页
SELECT * FROM emp 
	ORDER BY empno 
	LIMIT 0, 3;
-- 第2页
SELECT * FROM emp 
	ORDER BY empno 
	LIMIT 3, 3;
-- 第3页
SELECT * FROM emp 
	ORDER BY empno 
	LIMIT 6, 3;
-- 推导一个公式 
SELECT * FROM emp
	ORDER BY empno 
	LIMIT 每页显示记录数 * (第几页-1) , 每页显示记录数
	
-- 测试
SELECT job, COUNT(*) FROM emp GROUP BY job;
-- 显示雇员总数，以及获得补助的雇员数
SELECT COUNT(*) FROM emp  WHERE mgr IS NOT NULL;
SELECT MAX(sal) - MIN(sal) FROM emp;

Using grouping functions and grouping clauses

-- 增强group by 的使用

-- (1) 显示每种岗位的雇员总数、平均工资。
SELECT COUNT(*), AVG(sal), job 
	FROM emp 
	GROUP BY job; 
-- (2) 显示雇员总数，以及获得补助的雇员数。
--  思路: 获得补助的雇员数 就是 comm 列为非null, 就是count(列)，如果该列的值为null, 是不会统计 , SQL 非常灵活，需要我们动脑筋.
SELECT COUNT(*), COUNT(comm)
	FROM emp 

--  老师的扩展要求：统计没有获得补助的雇员数
SELECT COUNT(*), COUNT(IF(comm IS NULL, 1, NULL))
	FROM emp 

SELECT COUNT(*), COUNT(*) - COUNT(comm)
	FROM emp 

-- (3) 显示管理者的总人数。小技巧:尝试写->修改->尝试[正确的]
SELECT COUNT(DISTINCT mgr) 
	FROM emp; 

-- (4) 显示雇员工资的最大差额。
-- 思路： max(sal) - min(sal)
SELECT MAX(sal) - MIN(sal) 
	FROM emp;

SELECT * FROM e
mp;
select * from dept;



-- 应用案例：请统计各个部门group by 的平均工资 avg，
-- 并且是大于1000的 having，并且按照平均工资从高到低排序， order by
-- 取出前两行记录 limit 0, 2

SELECT deptno, AVG(sal) AS avg_sal
	FROM emp
	GROUP BY deptno
	HAVING  avg_sal > 1000
	ORDER BY avg_sal DESC
	LIMIT 0,2

Summary of Data Grouping

If the select statement also contains group by, having, limitorder by, then their order isgroup by , having , orderby, limit

mysql multi-table query

Multi-table query practice

By default: when two tables are queried, the rule

From the first table, take a row and combine it with each row of the second table, and return the result [contains all columns of the two tables].
The total number of records returned is the number of rows in the first table * the number of rows in the second table ( Cartesian product )

-- 多表查询
-- ?显示雇员名,雇员工资及所在部门的名字 【笛卡尔集】
/*
	1. 雇员名,雇员工资 来自 emp表
	2. 部门的名字 来自 dept表
	3. 需求对 emp 和 dept查询  ename,sal,dname,deptno
	4. 当我们需要指定显示某个表的列是，需要 表.列表
*/
SELECT ename,sal,dname,emp.deptno
	FROM emp, dept 
	WHERE emp.deptno = dept.deptno
	
select * from emp;
select * from dept;
select * from salgrade;
-- 小技巧：多表查询的条件不能少于 表的个数-1, 否则会出现笛卡尔集
-- ?如何显示部门号为10的部门名、员工名和工资 
-- 重复的deptno要标清是哪个表的
SELECT ename,sal,dname,emp.deptno
	FROM emp, dept 
	WHERE emp.deptno = dept.deptno and emp.deptno = 10

-- ?显示各个员工的姓名，工资，及其工资的级别

-- 思路 姓名，工资 来自 emp 13
--      工资级别 salgrade 5
-- 写sql , 先写一个简单，然后加入过滤条件...
select ename, sal, grade 
	from emp , salgrade
	where sal between losal and hisal;

self-join

Self-join refers to a join query on the same table [treating the same table as two tables].

-- 多表查询的 自连接

-- 思考题: 显示公司员工名字和他的上级的名字

-- 老韩分析： 员工名字 在emp, 上级的名字的名字 emp
-- 员工和上级是通过 emp 表的 mgr 列关联
-- 这里老师小结：
-- 自连接的特点 1. 把同一张表当做两张表使用
--             2. 需要给表取别名 表名  表别名 
-- 3. 列名不明确，可以指定列的别名 列名 as 列的别名		
SELECT worker.ename AS '职员名' ,  boss.ename AS '上级名'
	FROM emp worker, emp boss -- 同一张表用不同的别名
	WHERE worker.mgr = boss.empno;
SELECT * FROM emp;

mysql table subquery

what is a subquery

Subqueries refer to select statements embedded in other SQL statements, also called nested queries

single row subquery

A single row subquery is a subquery statement that returns only one row of data

multi-row subquery

A multi-row subquery refers to a subquery that returns multiple rows of data using keywordsin

-- 子查询的演示
-- 请思考：如何显示与SMITH同一部门的所有员工?
/*
	1. 先查询到 SMITH的部门号得到
	2. 把上面的select 语句当做一个子查询来使用
*/
SELECT deptno 
	FROM emp 
	WHERE ename = 'SMITH'

-- 下面的答案.	
SELECT * 
	FROM emp
	WHERE deptno = (
		SELECT deptno 
		FROM emp 
		WHERE ename = 'SMITH'
	)

-- 课堂练习:如何查询和部门10的工作相同的雇员的
-- 名字、岗位、工资、部门号, 但是不含10号部门自己的雇员.

/*
	1. 查询到10号部门有哪些工作
	2. 把上面查询的结果当做子查询使用
*/
select distinct job 
	from emp 
	where deptno = 10;
	
--  下面语句完整

select ename, job, sal, deptno
	from emp
	where job in (
		SELECT DISTINCT job 
		FROM emp 
		WHERE deptno = 10
	) and deptno <> 10

Subqueries are used as temporary tables

A subquery can be used as a temporary table

-- 子查询练习

-- 请思考：查找每个部门工资高于本部门平均工资的人的资料
-- 这里要用到数据查询的小技巧，把一个子查询当作一个临时表使用

-- 1. 先得到每个部门的 部门号和 对应的平均工资

SELECT deptno, AVG(sal) AS avg_sal
	FROM emp GROUP BY deptno
	
-- 2. 把上面的结果当做子查询，作为temp表, 和 emp 进行多表查询    
SELECT ename, sal, temp.avg_sal, emp.deptno
	FROM emp, (
		SELECT deptno, AVG(sal) AS avg_sal
		FROM emp 
		GROUP BY deptno
	) temp 
	where emp.deptno = temp.deptno and emp.sal > temp.avg_sal
	
-- 查找每个部门工资最高的人的详细资料

SELECT ename, sal, temp.max_sal, emp.deptno
	FROM emp, (
		SELECT deptno, max(sal) AS max_sal
		FROM emp 
		GROUP BY deptno
	) temp 
	WHERE emp.deptno = temp.deptno AND emp.sal = temp.max_sal
	

-- 查询每个部门的信息(包括：部门名,编号,地址)和人员数量,我们一起完成。

-- 1. 部门名,编号,地址 来自 dept表
-- 2. 各个部门的人员数量 -》 构建一个临时表

select count(*), deptno 
	from emp
	group by deptno;
	

select dname, dept.deptno, loc , tmp.per_num as '人数'
	from dept, (
		SELECT COUNT(*) as per_num, deptno 
		FROM emp
		GROUP BY deptno
	) tmp 
	where tmp.deptno = dept.deptno

-- 还有一种写法 表.* 表示将该表所有列都显示出来, 可以简化sql语句
-- 在多表查询中，当多个表的列不重复时，才可以直接写列名

SELECT tmp.* , dname, loc
	FROM dept, (
		SELECT COUNT(*) AS per_num, deptno 
		FROM emp
		GROUP BY deptno
	) tmp 
	WHERE tmp.deptno = dept.deptno

Using the all operator in a multi-row subquery

Using the any operator in a multi-row subquery

-- all 和 any的使用

-- 请思考:显示工资比部门30的所有员工的工资高的员工的姓名、工资和部门号

SELECT ename, sal, deptno
	FROM emp
	WHERE sal > ALL(
		SELECT sal 
			FROM emp
			WHERE deptno = 30
		) 
-- 可以这样写
SELECT ename, sal, deptno
	FROM emp
	WHERE sal > (
		SELECT MAX(sal) 
			FROM emp
			WHERE deptno = 30
		) 

-- 请思考:如何显示工资比部门30的其中一个员工的工资高的员工的姓名、工资和部门号

SELECT ename, sal, deptno
	FROM emp
	WHERE sal > any(
		SELECT sal 
			FROM emp
			WHERE deptno = 30
		)

 SELECT ename, sal, deptno
	FROM emp
	WHERE sal > (
		SELECT min(sal) 
			FROM emp
			WHERE deptno = 30
		)


-- 查询ecshop中各个类别中，价格最高的商品

-- 查询 商品表
-- 先得到 各个类别中，价格最高的商品 max + group by cat_id, 当做临时表
-- 把子查询当做一张临时表可以解决很多很多复杂的查询

select cat_id , max(shop_price) 
	from ecs_goods
	group by cat_id
	
	
-- 这个最后答案	
select goods_id, ecs_goods.cat_id, goods_name, shop_price 
	from (
		SELECT cat_id , MAX(shop_price) as max_price
		FROM ecs_goods
		GROUP BY cat_id
	) temp , ecs_goods
	where  temp.cat_id = ecs_goods.cat_id 
	and temp.max_price = ecs_goods.shop_price

multi-column subquery

Multi-column subquery refers to a subquery statement that returns data in multiple columns

-- 多列子查询

-- 请思考如何查询与allen的部门和岗位完全相同的所有雇员(并且不含allen本人)
-- (字段1， 字段2 ...) = (select 字段 1，字段2 from 。。。。)

-- 分析: 1. 得到smith的部门和岗位

SELECT deptno , job
	FROM emp 
	WHERE ename = 'ALLEN'
	
-- 分析: 2  把上面的查询当做子查询来使用，并且使用多列子查询的语法进行匹配
SELECT * 
	FROM emp
	WHERE (deptno , job) = (
		SELECT deptno , job
		FROM emp 
		WHERE ename = 'ALLEN'
	) AND ename != 'ALLEN'



-- 请查询 和宋江数学，英语，语文   
-- 成绩 完全相同的学生
SELECT * 
	FROM student
	WHERE (math, english, chinese) = (
		SELECT math, english, chinese
		FROM student
		WHERE `name` = '宋江'
	)

SELECT * FROM student;

Using a subquery in the from clause

-- 子查询练习

-- 请思考：查找每个部门工资高于本部门平均工资的人的资料
-- 这里要用到数据查询的小技巧，把一个子查询当作一个临时表使用

-- 1. 先得到每个部门的 部门号和 对应的平均工资

SELECT deptno, AVG(sal) AS avg_sal
	FROM emp GROUP BY deptno
	
-- 2. 把上面的结果当做子查询, 和 emp 进行多表查询
--    
SELECT ename, sal, temp.avg_sal, emp.deptno
	FROM emp, (
		SELECT deptno, AVG(sal) AS avg_sal
		FROM emp 
		GROUP BY deptno
	) temp 
	where emp.deptno = temp.deptno and emp.sal > temp.avg_sal
	
-- 查找每个部门工资最高的人的详细资料

SELECT ename, sal, temp.max_sal, emp.deptno
	FROM emp, (
		SELECT deptno, max(sal) AS max_sal
		FROM emp 
		GROUP BY deptno
	) temp 
	WHERE emp.deptno = temp.deptno AND emp.sal = temp.max_sal
	

-- 查询每个部门的信息(包括：部门名,编号,地址)和人员数量,我们一起完成。

-- 1. 部门名,编号,地址 来自 dept表
-- 2. 各个部门的人员数量 -》 构建一个临时表

select count(*), deptno 
	from emp
	group by deptno;
	

select dname, dept.deptno, loc , tmp.per_num as '人数'
	from dept, (
		SELECT COUNT(*) as per_num, deptno 
		FROM emp
		GROUP BY deptno
	) tmp 
	where tmp.deptno = dept.deptno

-- 还有一种写法 表.* 表示将该表所有列都显示出来, 可以简化sql语句
-- 在多表查询中，当多个表的列不重复时，才可以直接写列名

SELECT tmp.* , dname, loc
	FROM dept, (
		SELECT COUNT(*) AS per_num, deptno 
		FROM emp
		GROUP BY deptno
	) tmp 
	WHERE tmp.deptno = dept.deptno

table replication

Self-replicating data (worm replication)

Sometimes, in order to test the efficiency of a certain SQL statement, when we need massive data, we can use this method to create massive data for the table.

-- 表的复制
-- 为了对某个sql语句进行效率测试，我们需要海量数据时，可以使用此法为表创建海量数据

CREATE TABLE my_tab01 
	( id INT,
	  `name` VARCHAR(32),
	  sal DOUBLE,
	  job VARCHAR(32),
	  deptno INT);
DESC my_tab01
SELECT * FROM my_tab01;

-- 演示如何自我复制
-- 1. 先把emp 表的记录复制到 my_tab01
INSERT INTO my_tab01 
	(id, `name`, sal, job,deptno)
	SELECT empno, ename, sal, job, deptno FROM emp;
-- 2. 自我复制
INSERT INTO my_tab01
	SELECT * FROM my_tab01;
SELECT COUNT(*) FROM my_tab01;

-- 如何删除掉一张表重复记录
-- 1. 先创建一张表 my_tab02, 
-- 2. 让 my_tab02 有重复的记录

CREATE TABLE my_tab02 LIKE emp; -- 这个语句 把emp表的结构(列)，复制到my_tab02

desc my_tab02;

insert into my_tab02
	select * from emp;
select * from my_tab02;
-- 3. 考虑去重 my_tab02的记录
/*
	思路 
	(1) 先创建一张临时表 my_tmp , 该表的结构和 my_tab02一样
	(2) 把my_tmp 的记录 通过 distinct 关键字 处理后 把记录复制到 my_tmp
	(3) 清除掉 my_tab02 记录
	(4) 把 my_tmp 表的记录复制到 my_tab02
	(5) drop 掉 临时表my_tmp
*/
-- (1) 先创建一张临时表 my_tmp , 该表的结构和 my_tab02一样

create table my_tmp like my_tab02
-- (2) 把my_tmp 的记录 通过 distinct 关键字 处理后 把记录复制到 my_tmp
insert into my_tmp 
	select distinct * from my_tab02;

-- (3) 清除掉 my_tab02 记录
delete from my_tab02;
-- (4) 把 my_tmp 表的记录复制到 my_tab02
insert into my_tab02
	select * from my_tmp;
-- (5) drop 掉 临时表my_tmp
drop table my_tmp;

select * from my_tab02;

combined query

introduce

Sometimes in practical applications, in order to combine the results of multiple selectstatements , you can use the set operator symbol union, union all.

union all: This operator is used to obtain the union of two result sets. Duplicate rows are not canceled when this operator is used.
union: This operation is similar to union all, but it will automatically remove duplicate rows in the result set

-- 合并查询
SELECT ename,sal,job FROM emp WHERE sal>2500 -- 5
SELECT ename,sal,job FROM emp WHERE job='MANAGER' -- 3

-- union all 就是将两个查询结果合并，不会去重
SELECT ename,sal,job FROM emp WHERE sal>2500 -- 5
UNION ALL
SELECT ename,sal,job FROM emp WHERE job='MANAGER' -- 3

-- union  就是将两个查询结果合并，会去重
SELECT ename,sal,job FROM emp WHERE sal>2500 -- 5
UNION 
SELECT ename,sal,job FROM emp WHERE job='MANAGER' -- 3

mysql table connection

The query we learned earlier is to use the where clause to filter the Cartesian product formed by two or more tables. According to the association conditions, all matching records are displayed, and those that cannot be matched are not displayed. For example: list the names of departments and the names and jobs of employees in these departments, and at the same time require to show those departments without employees.

outer join

Left outer join (if the table on the left is fully displayed, we say it is a left outer join)
Right outer join (if the table on the right is fully displayed, we say it is a right outer join)

Use left join (display everyone's results, if there is no result, also display the person's name and id number, the result is displayed as empty) select ... from table 1 left join table 2 on condition [table 1: is the left table table 2 : is the right table].
Use right outer join (display all grades, if there is no name match, display empty)
select ... from table 1 right join table 2 on condition [table 1: is the left table table 2: is the right table]

-- 外连接

-- 比如：列出部门名称和这些部门的员工名称和工作，
-- 同时要求 显示出那些没有员工的部门。

-- 使用我们学习过的多表查询的SQL， 看看效果如何?

SELECT dname, ename, job 
	FROM emp, dept
	WHERE emp.deptno = dept.deptno
	ORDER BY dname
SELECT * FROM dept;

SELECT * FROM emp;


-- 创建 stu
/*
id  name   
1   Jack
2   Tom
3   Kity
4   nono
*/
CREATE TABLE stu (
	id INT,
	`name` VARCHAR(32));
INSERT INTO stu VALUES(1, 'jack'),(2,'tom'),(3, 'kity'),(4, 'nono');
SELECT * FROM stu;
-- 创建 exam
/*
id   grade
1    56
2    76
11   8

*/
CREATE TABLE exam(
	id INT,
	grade INT);
INSERT INTO exam VALUES(1, 56),(2,76),(11, 8);
SELECT * FROM exam;

-- 使用左连接
-- （显示所有人的成绩，如果没有成绩，也要显示该人的姓名和id号,成绩显示为空）

SELECT `name`, stu.id, grade
	FROM stu, exam
	WHERE stu.id = exam.id;
	
-- 改成左外连接
SELECT `name`, stu.id, grade
	FROM stu LEFT JOIN exam
	ON stu.id = exam.id;
	
	
-- 使用右外连接（显示所有成绩，如果没有名字匹配，显示空)
-- 即：右边的表(exam) 和左表没有匹配的记录，也会把右表的记录显示出来
SELECT `name`, stu.id, grade
	FROM stu RIGHT JOIN exam
	ON stu.id = exam.id;

-- 列出部门名称和这些部门的员工信息(名字和工作)，
-- 同时列出那些没有员工的部门名。5min
-- 使用左外连接实现
SELECT dname, ename, job
	FROM dept LEFT JOIN emp
	ON dept.deptno = emp.deptno
	
-- 使用右外连接实现

SELECT dname, ename, job
	FROM emp RIGHT JOIN dept
	ON dept.deptno = emp.deptno

mysql constraints

basic introduction

Constraints are used to ensure that the data in a database satisfies specific business rules. In mysql, constraints include: not null, unique, primary key, foreign key, and check.

primary key (primary key)

Field name field type primary key (indicates that the field is the primary key)

It is used to uniquely mark the data of the table row. When the primary key constraint is defined, the column cannot be repeated

The primary key cannot be repeated and cannot be null.
A table can have at most one primary key, but it can be a composite primary key
There are two ways to specify the primary key
- Specify directly after the field name: field name primakry key
- Write the primary key (column name) at the end of the table definition;
Using the desc table name , you can see the primary key.
In actual development, each table is often designed with a primary key.

-- 主键使用

-- id	name 	email
CREATE TABLE t17
	(id INT PRIMARY KEY, -- 表示id列是主键 
	`name` VARCHAR(32),
	email VARCHAR(32));
	
-- 主键列的值是不可以重复
INSERT INTO t17
	VALUES(1, 'jack', '[email protected]');
INSERT INTO t17
	VALUES(2, 'tom', '[email protected]');

INSERT INTO t17
	VALUES(1, 'hsp', '[email protected]'); -- 报错
	
SELECT * FROM t17;

-- 主键使用的细节讨论
-- primary key不能重复而且不能为 null。
INSERT INTO t17
	VALUES(NULL, 'hsp', '[email protected]');
-- 一张表最多只能有一个主键, 但可以是复合主键(比如 id+name)
CREATE TABLE t18
	(id INT PRIMARY KEY, -- 表示id列是主键 
	`name` VARCHAR(32), PRIMARY KEY -- 错误的
	email VARCHAR(32));
-- 演示复合主键 (id 和 name 做成复合主键)
CREATE TABLE t18
	(id INT , 
	`name` VARCHAR(32), 
	email VARCHAR(32),
	PRIMARY KEY (id, `name`) -- 这里就是复合主键
	);

INSERT INTO t18
	VALUES(1, 'tom', '[email protected]');
INSERT INTO t18
	VALUES(1, 'jack', '[email protected]');
INSERT INTO t18
	VALUES(1, 'tom', '[email protected]'); -- 这里就违反了复合主键
SELECT * FROM t18;

-- 主键的指定方式 有两种 
-- 1. 直接在字段名后指定：字段名  primakry key
-- 2. 在表定义最后写 primary key(列名); 
CREATE TABLE t19
	(id INT , 
	`name` VARCHAR(32) PRIMARY KEY, 
	email VARCHAR(32)
	);

CREATE TABLE t20
	(id INT , 
	`name` VARCHAR(32) , 
	email VARCHAR(32),
	PRIMARY KEY(`name`) -- 在表定义最后写 primary key(列名)
	);
 
-- 使用desc 表名，可以看到primary key的情况

DESC t20 -- 查看 t20表的结果，显示约束的情况
DESC t18

not null

If not null is defined on the column, then the column must be supplied with data when inserting data.

字段名字段类型 not null

unique (unique)

When a unique constraint is defined, the column values cannot be repeated.

字段名字段类型 unique

If not null is not specified, the unique field can have multiple nulls
A table can have multiple unique fields

-- unique的使用

CREATE TABLE t21
	(id INT UNIQUE ,  -- 表示 id 列是不可以重复的.
	`name` VARCHAR(32) , 
	email VARCHAR(32)
	);
	
INSERT INTO t21
	VALUES(1, 'jack', '[email protected]');

INSERT INTO t21
	VALUES(1, 'tom', '[email protected]');
	
-- unqiue使用细节
-- 1. 如果没有指定 not null , 则 unique 字段可以有多个null
-- 如果一个列(字段)， 是 unique not null 使用效果类似 primary key
INSERT INTO t21
	VALUES(NULL, 'tom', '[email protected]');
SELECT * FROM t21;
-- 2. 一张表可以有多个unique字段

CREATE TABLE t22
	(id INT UNIQUE ,  -- 表示 id 列是不可以重复的.
	`name` VARCHAR(32) UNIQUE , -- 表示name不可以重复 
	email VARCHAR(32)
	);
DESC t22

foreign key (foreign key)

Used to define the relationship between master and slave tables:

The foreign key constraint must be defined on the secondary table, and the primary table must have a primary key constraint or a unique constraint,
When the foreign key constraint is defined, it is required that the foreign key column data must exist in the primary key column of the main table or be null (student/class icon).

-- 外键演示

-- 创建 主表 my_class
CREATE TABLE my_class (
	id INT PRIMARY KEY , -- 班级编号
	`name` VARCHAR(32) NOT NULL DEFAULT '');

-- 创建 从表 my_stu
CREATE TABLE my_stu (
	id INT PRIMARY KEY , -- 学生编号
	`name` VARCHAR(32) NOT NULL DEFAULT '',
	class_id INT , -- 学生所在班级的编号
	-- 下面指定外键关系
	FOREIGN KEY (class_id) REFERENCES my_class(id))
-- 测试数据
INSERT INTO my_class 
	VALUES(100, 'java'), (200, 'web');
INSERT INTO my_class 
	VALUES(300, 'php');
	
SELECT * FROM my_class;
INSERT INTO my_stu 
	VALUES(1, 'tom', 100);
INSERT INTO my_stu 
	VALUES(2, 'jack', 200);
INSERT INTO my_stu 
	VALUES(3, 'hsp', 300);
INSERT INTO my_stu 
	VALUES(4, 'mary', 400); -- 这里会失败...因为400班级不存在

INSERT INTO my_stu 
	VALUES(5, 'king', NULL); -- 可以, 外键 没有写 not null
SELECT * FROM my_class;

-- 一旦建立主外键的关系，数据不能随意删除了
DELETE FROM my_class
	WHERE id = 100;

check

It is used to enforce the conditions that the row data must meet. Assume that the check constraint is defined on the sal column, and the value of the sal column is required to be between 1000 and 2000. If it is not between 1000 and 2000, an error will be prompted.

Tip: both Oracle and SQL Server support check, but mysql5.7 does not support check at present, only for syntax verification, but it will not take effect.

-- 演示check的使用
-- mysql5.7目前还不支持check ,只做语法校验，但不会生效
-- 了解 
-- 学习 oracle, sql server, 这两个数据库是真的生效.

-- 测试
CREATE TABLE t23 (
	id INT PRIMARY KEY,
	`name` VARCHAR(32) ,
	sex VARCHAR(6) CHECK (sex IN('man','woman')),
	sal DOUBLE CHECK ( sal > 1000 AND sal < 2000)
	);
	
-- 添加数据
INSERT INTO t23 
	VALUES(1, 'jack', 'mid', 1);
SELECT * FROM t23;

Store vending system table design case

-- 使用约束的课堂练习

CREATE DATABASE shop_db;

-- 现有一个商店的数据库shop_db，记录客户及其购物情况，由下面三个表组成：
-- 商品goods（商品号goods_id，商品名goods_name，单价unitprice，商品类别category，供应商provider);
-- 客户customer（客户号customer_id,姓名name,住址address,电邮email性别sex,身份证card_Id);
-- 购买purchase（购买订单号order_id，客户号customer_id,商品号goods_id,购买数量nums);
-- 1 建表，在定义中要求声明 [进行合理设计]：
-- (1)每个表的主外键；
-- (2)客户的姓名不能为空值；
-- (3)电邮不能够重复;
-- (4)客户的性别[男|女] check 枚举..
-- (5)单价unitprice 在 1.0 - 9999.99 之间 check

-- 商品goods
CREATE TABLE goods (
	goods_id INT PRIMARY KEY,
	goods_name VARCHAR(64) NOT NULL DEFAULT '',
	unitprice DECIMAL(10,2) NOT NULL DEFAULT 0 
		CHECK (unitprice >= 1.0 AND unitprice <= 9999.99),
	category INT NOT NULL DEFAULT 0,
	provider VARCHAR(64) NOT NULL DEFAULT '');
	
-- 客户customer（客户号customer_id,姓名name,住址address,电邮email性别sex,
-- 身份证card_Id);
CREATE TABLE customer(
	customer_id CHAR(8) PRIMARY KEY, -- 程序员自己决定
	`name` VARCHAR(64) NOT NULL DEFAULT '',
	address VARCHAR(64) NOT NULL DEFAULT '',
	email VARCHAR(64) UNIQUE NOT NULL,
	sex ENUM('男','女') NOT NULL ,  -- 这里老师使用的枚举类型, 是生效
	card_Id CHAR(18)); 
	
-- 购买purchase（购买订单号order_id，客户号customer_id,商品号goods_id,
-- 购买数量nums);
CREATE TABLE purchase(
	order_id INT UNSIGNED PRIMARY KEY,
	customer_id CHAR(8) NOT NULL DEFAULT '', -- 外键约束在后
	goods_id INT NOT NULL DEFAULT 0 , -- 外键约束在后
	nums INT NOT NULL DEFAULT 0,
	FOREIGN KEY (customer_id) REFERENCES customer(customer_id),
	FOREIGN KEY (goods_id) REFERENCES goods(goods_id));
DESC goods;
DESC customer;
DESC purchase;

Self Growth

Basic introduction to self-growth

In a certain table, there is an id column (integer), we hope that when adding a record, the column starts from 1 and grows automatically, how to deal with it?

Self-growth usage details

Generally speaking, self-growth is used in conjunction with the primary key
Self-growth can also be used alone [but it needs to be combined with a unique]
The self-growth modified field is an integer type (although decimals can also be used, it is very, very rarely used in this way)
Self-growth starts from 1 by default, you can also modify it by the following commandalter table 表名auto_increment = 新的开始值;
If you specify a value for the self-growth field (column) when you add data, the specified value shall prevail. **If self-growth is specified, generally speaking, follow the rules of self-growth (starting from the specified value , and then self-growth)** to add data

-- 演示自增长的使用
-- 创建表
CREATE TABLE t24
	(id INT PRIMARY KEY AUTO_INCREMENT,
	 email VARCHAR(32)NOT NULL DEFAULT '',
	 `name` VARCHAR(32)NOT NULL DEFAULT ''); 
DESC t24
-- 测试自增长的使用
INSERT INTO t24
	VALUES(NULL, '[email protected]', 'tom'); -- 没有给值，自动维护，id自增长

INSERT INTO t24
	(email, `name`) VALUES('[email protected]', 'hsp');

SELECT * FROM t24;

-- 修改默认的自增长开始值
ALTER TABLE t25 AUTO_INCREMENT = 100
CREATE TABLE t25
	(id INT PRIMARY KEY AUTO_INCREMENT,
	 email VARCHAR(32)NOT NULL DEFAULT '',
	 `name` VARCHAR(32)NOT NULL DEFAULT ''); 
INSERT INTO t25
	VALUES(NULL, '[email protected]', 'mary');
INSERT INTO t25
	VALUES(666, '[email protected]', 'hsp');
SELECT * FROM t25;

CREATE DATABASE tmp;
CREATE TABLE dept( /*部门表*/
deptno MEDIUMINT   UNSIGNED  NOT NULL  DEFAULT 0,
dname VARCHAR(20)  NOT NULL  DEFAULT "",
loc VARCHAR(13) NOT NULL DEFAULT ""
) ;

#创建表EMP雇员
CREATE TABLE emp
(empno  MEDIUMINT UNSIGNED  NOT NULL  DEFAULT 0, /*编号*/
ename VARCHAR(20) NOT NULL DEFAULT "", /*名字*/
job VARCHAR(9) NOT NULL DEFAULT "",/*工作*/
mgr MEDIUMINT UNSIGNED NOT NULL DEFAULT 0,/*上级编号*/
hiredate DATE NOT NULL,/*入职时间*/
sal DECIMAL(7,2)  NOT NULL,/*薪水*/
comm DECIMAL(7,2) NOT NULL,/*红利*/
deptno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0 /*部门编号*/
) ;

#工资级别表
CREATE TABLE salgrade
(
grade MEDIUMINT UNSIGNED NOT NULL DEFAULT 0,
losal DECIMAL(17,2)  NOT NULL,
hisal DECIMAL(17,2)  NOT NULL
);

#测试数据
INSERT INTO salgrade VALUES (1,700,1200);
INSERT INTO salgrade VALUES (2,1201,1400);
INSERT INTO salgrade VALUES (3,1401,2000);
INSERT INTO salgrade VALUES (4,2001,3000);
INSERT INTO salgrade VALUES (5,3001,9999);

mysql index

Indexing Quick Start

Indexes are the most cost-effective thing to improve database performance. No need to add memory , no need to change programs, no need to adjust sql, the query speed may be increased by hundreds of times and thousands of times.

CREATE INDEX ename_index ON emp (ename) -- 在 ename 上创建索引

-- 创建测试数据库 tmp
CREATE DATABASE tmp;

CREATE TABLE dept( /*部门表*/
deptno MEDIUMINT   UNSIGNED  NOT NULL  DEFAULT 0,
dname VARCHAR(20)  NOT NULL  DEFAULT "",
loc VARCHAR(13) NOT NULL DEFAULT ""
) ;

#创建表EMP雇员
CREATE TABLE emp
(empno  MEDIUMINT UNSIGNED  NOT NULL  DEFAULT 0, /*编号*/
ename VARCHAR(20) NOT NULL DEFAULT "", /*名字*/
job VARCHAR(9) NOT NULL DEFAULT "",/*工作*/
mgr MEDIUMINT UNSIGNED NOT NULL DEFAULT 0,/*上级编号*/
hiredate DATE NOT NULL,/*入职时间*/
sal DECIMAL(7,2)  NOT NULL,/*薪水*/
comm DECIMAL(7,2) NOT NULL,/*红利*/
deptno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0 /*部门编号*/
) ;

#工资级别表
CREATE TABLE salgrade
(
grade MEDIUMINT UNSIGNED NOT NULL DEFAULT 0,
losal DECIMAL(17,2)  NOT NULL,
hisal DECIMAL(17,2)  NOT NULL
);

#测试数据
INSERT INTO salgrade VALUES (1,700,1200);
INSERT INTO salgrade VALUES (2,1201,1400);
INSERT INTO salgrade VALUES (3,1401,2000);
INSERT INTO salgrade VALUES (4,2001,3000);
INSERT INTO salgrade VALUES (5,3001,9999);

DELIMITER $$

#创建一个函数，名字 rand_string，可以随机返回我指定的个数字符串
CREATE FUNCTION rand_string(n INT)
RETURNS VARCHAR(255) #该函数会返回一个字符串
BEGIN
#定义了一个变量 chars_str， 类型  varchar(100)
#默认给 chars_str 初始值   'abcdefghijklmnopqrstuvwxyzABCDEFJHIJKLMNOPQRSTUVWXYZ'
 DECLARE chars_str VARCHAR(100) DEFAULT
   'abcdefghijklmnopqrstuvwxyzABCDEFJHIJKLMNOPQRSTUVWXYZ'; 
 DECLARE return_str VARCHAR(255) DEFAULT '';
 DECLARE i INT DEFAULT 0; 
 WHILE i < n DO
    # concat 函数 : 连接函数mysql函数
   SET return_str =CONCAT(return_str,SUBSTRING(chars_str,FLOOR(1+RAND()*52),1));
   SET i = i + 1;
   END WHILE;
  RETURN return_str;
  END $$


 #这里我们又自定了一个函数,返回一个随机的部门号
CREATE FUNCTION rand_num( )
RETURNS INT(5)
BEGIN
DECLARE i INT DEFAULT 0;
SET i = FLOOR(10+RAND()*500);
RETURN i;
END $$

 #创建一个存储过程， 可以添加雇员
CREATE PROCEDURE insert_emp(IN START INT(10),IN max_num INT(10))
BEGIN
DECLARE i INT DEFAULT 0;
#set autocommit =0 把autocommit设置成0
 #autocommit = 0 含义: 不要自动提交
 SET autocommit = 0; #默认不提交sql语句
 REPEAT
 SET i = i + 1;
 #通过前面写的函数随机产生字符串和部门编号，然后加入到emp表
 INSERT INTO emp VALUES ((START+i) ,rand_string(6),'SALESMAN',0001,CURDATE(),2000,400,rand_num());
  UNTIL i = max_num
 END REPEAT;
 #commit整体提交所有sql语句，提高效率
   COMMIT;
 END $$

 #添加8000000数据
CALL insert_emp(100001,8000000)$$

#命令结束符，再重新设置为;
DELIMITER ;

SELECT COUNT(*) FROM emp;

-- 在没有创建索引时，我们的查询一条记录
SELECT * 
	FROM emp 
	WHERE empno = 1234567 
-- 使用索引来优化一下， 体验索引的牛

-- 在没有创建索引前 , emp.ibd 文件大小 是 524m
-- 创建索引后 emp.ibd 文件大小 是 655m [索引本身也会占用空间.]
-- 创建ename列索引,emp.ibd 文件大小 是 827m

-- empno_index 索引名称 
-- ON emp (empno) : 表示在 emp表的 empno列创建索引
CREATE INDEX empno_index ON emp (empno)

-- 创建索引后， 查询的速度如何

SELECT * 
	FROM emp 
	WHERE empno = 1234578 -- 0.003s 原来是4.5s


-- 创建索引后，只对创建了索引的列有效 
SELECT * 
	FROM emp 
	WHERE ename = 'PjDlwy' -- 没有在ename创建索引时，时间4.7s

CREATE INDEX ename_index ON emp (ename) -- 在ename上创建索引

The principle of indexing

Why is it slow without an index? Because of the full table scan.

Why is it faster to use an index? Form an indexed data structure, such as a binary tree index (the cost is as follows)

disk usage
Affects the efficiency of the dml (update delete insert) statement. Deletion or insertion will affect the data structure and may be refactored.

indexed class

Primary key index, the primary key is automatically the primary index (type Primary key)
Unique index (UNIQUE)
Ordinary index (INDEX)
Full text index (FULLTEXT) [for MyISAM]

For general development, do not use the full-text index that comes with mysql, but use: Full-text search framework: Solr and ElasticSearch ( ES )

create table t1(
id int primary key, -- 主键，同时也是索引，称为主键索引.
    name varchar(32));
create table t2(
id int unique, -- id是唯一的，同时也是索引，称为unique索引.

index use

1. Add index (build small table test id, name)

create [UNIQUE] index index_name on tbl_name (col_ name [(length)][ASC | DESC],......);
alter table table_name ADD INDEX [index_namel (index_col_name,..)

2. Add primary key (index)

ALTER TABLE 表名 ADD PRIMARY KEY(列名...);

3. Delete the index

DROP INDEX index_name ON tbl_name,
alter table table_name drop index index_name;

4. Deleting the primary key index is special:

alter table t_b drop primary key;

5. Query index (three ways)

show index(es) from table_name;
show keys from table_name;
desc table_Name;

-- 演示mysql的索引的使用
-- 创建索引
CREATE TABLE t25 (
	id INT ,
	`name` VARCHAR(32));
	
-- 查询表是否有索引
SHOW INDEXES FROM t25;
-- 添加索引
-- 添加唯一索引 
CREATE UNIQUE INDEX id_index ON t25 (id);
-- 添加普通索引方式1
CREATE INDEX id_index ON t25 (id);
-- 如何选择 
-- 1. 如果某列的值，是不会重复的，则优先考虑使用unique索引, 否则使用普通索引
-- 添加普通索引方式2
ALTER TABLE t25 ADD INDEX id_index (id)

-- 添加主键索引
CREATE TABLE t26 (
	id INT ,
	`name` VARCHAR(32));
ALTER TABLE t26 ADD PRIMARY KEY (id)

SHOW INDEX FROM t25

-- 删除索引
DROP INDEX id_index ON t25
-- 删除主键索引
ALTER TABLE t26 DROP PRIMARY KEY


-- 修改索引 ，先删除，在添加新的索引

-- 查询索引
-- 1. 方式
SHOW INDEX FROM t25
-- 2. 方式
SHOW INDEXES FROM t25
-- 3. 方式
SHOW KEYS FROM t25
-- 4 方式
DESC t25

Which columns are suitable for indexing

More frequently as a query condition field should create an index
```
select * from emp where empno = 1
```
Fields with poor uniqueness are not suitable for creating indexes alone, even if they are frequently used as query conditions
```
select * from emp where sex =‘男‘
```
Fields that are updated very frequently are not suitable for indexing
```
select* from emp where logincount = 1
```
Fields that do not appear in the WHERE clause should not be indexed

mysql transaction

what is a transaction

Transactions are used to ensure data consistency. It consists of a group of related dml (data manipulation language addition, deletion and modification) statements. The dml statements in this group either all succeed or all fail. For example, transfers must be processed with transactions to ensure data consistency.

Schematic diagram:

-- 事务的一个重要的概念和具体操作
-- 演示
-- 1. 创建一张测试表
CREATE TABLE t27
	( id INT,
	  `name` VARCHAR(32));
-- 2. 开始事务
START TRANSACTION 
-- 3. 设置保存点
SAVEPOINT a
-- 执行dml 操作
INSERT INTO t27 VALUES(100, 'tom');
SELECT * FROM t27;

SAVEPOINT b
-- 执行dml操作
INSERT INTO t27 VALUES(200, 'jack');

-- 回退到 b
ROLLBACK TO b
-- 继续回退 a
ROLLBACK TO a
-- 如果这样, 表示直接回退到事务开始的状态.
ROLLBACK 
COMMIT

Transactions and Locks

When executing a transaction operation (dml statement), mysql will lock the table to prevent other users from changing the data in the table, which is very important for users.

Several important operations of mysql data center console transaction

start transaction-- start a transaction
savepointsavepoint name – set a savepoint
rollback tosave roll call – rollback transaction
rollback-- Roll back all transactions
commit– Submit the transaction, all operations take effect, and cannot be rolled back

rollback transaction

Before introducing the rollback transaction, first introduce the savepoint (savepoint). The savepoint is a point in the transaction, which is used to cancel some transactions. When the transaction ends (commit), all the savepoints defined by the transaction will be automatically deleted. When performing a rollback transaction, you can roll back to a specified point by specifying a savepoint.

commit transaction

The commit statement can be used to commit the transaction. When the commit statement is executed, the change of the transaction will be confirmed, the transaction will be ended, the savepoint will be deleted, the lock will be released, and the data will take effect. After using the commit statement to end the transaction, other sessions [ other connections ] will be able to check the new data after the transaction change [all data will officially take effect.]

Business Details Discussion

If you do not start a transaction, by default, dml operations are committed automatically and cannot be rolled back.
If you start a transaction, you have not created a savepoint. You can perform a rollback, and the default is to roll back to the state where your transaction started.
You can also create multiple savepoints in this transaction (not yet committed). For example: savepoint
aaa; execute dml, savepoint bbb;
You can choose which savepoint to roll back to before the transaction is committed.
The transaction mechanism of mysql needs the storage engine of innodb to be used, and myisam is not easy to use .
Start a transaction start transaction or you can write set autocommit=off;

-- 讨论 事务细节
-- 1. 如果不开始事务，默认情况下，dml操作是自动提交的，不能回滚
INSERT INTO t27 VALUES(300, 'milan'); -- 自动提交 commit

SELECT * FROM t27

-- 2. 如果开始一个事务，你没有创建保存点. 你可以执行 rollback，
-- 默认就是回退到你事务开始的状态
START TRANSACTION 
INSERT INTO t27 VALUES(400, 'king');
INSERT INTO t27 VALUES(500, 'scott');
ROLLBACK -- 表示直接回退到事务开始的的状态
COMMIT;

-- 3. 你也可以在这个事务中(还没有提交时), 创建多个保存点.比如: savepoint 	aaa;    
-- 执行 dml , savepoint  bbb

-- 4. 你可以在事务没有提交前，选择回退到哪个保存点
-- 5. InnoDB 存储引擎支持事务 , MyISAM 不支持
-- 6. 开始一个事务 start  transaction 或者可以写 set autocommit=off;

mysql transaction isolation level

Introduction to Transaction Isolation Levels

When multiple connections open their own transactions to operate data in the database, the database system is responsible for isolating operations to ensure the accuracy of each connection when obtaining data. (Popular explanation: each transaction sees different data in the same table)
If isolation is not considered, the following problems may arise:

dirty read
non-repeatable read
Phantom reading

View transaction isolation level

Dirty read: When a transaction reads changes (update, insert, delete) that have not yet been committed by another transaction, a dirty read occurs. (uncommitted)
Non-repeatable read (nonrepeatable read): The same query is performed multiple times in the same transaction. Due to modifications or deletions made by other submitted transactions, different result sets are returned each time, and non-repeatable reads occur at this time. (committed)
Phantom read: The same query is performed multiple times in the same transaction, and a different result set is returned each time due to the insert operations performed by other committed transactions, and phantom reads occur at this time. (committed)

transaction isolation level

Concept: Mysql isolation level defines the degree of isolation between transactions.

Locking will not operate the database when other threads operate the database, and get stuck, waiting for other threads to commit before entering the database.

mysql transaction isolation level – case

-- 演示mysql的事务隔离级别

-- 1. 开了两个mysql的控制台
-- 2. 查看当前mysql的隔离级别
SELECT @@tx_isolation;

-- mysql> SELECT @@tx_isolation;
-- +-----------------+
-- | @@tx_isolation  |
-- +-----------------+
-- | REPEATABLE-READ |
-- +-----------------+

-- 3.把其中一个控制台的隔离级别设置 Read uncommitted

SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED

-- 4. 创建表
CREATE TABLE `account`(
	id INT,
	`name` VARCHAR(32),
	money INT);
	

-- 查看当前会话隔离级别 
SELECT @@tx_isolation
-- 查看系统当前隔离级别
SELECT @@global.tx_isolation
-- 设置当前会话隔离级别
SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
-- 设置系统当前隔离级别
SET GLOBAL TRANSACTION ISOLATION LEVEL [你设置的级别]

Set transaction isolation level

View the current session isolation level
```
select @@tx_isolation;
```
View the current isolation level of the system
```
select @@global.tx_isolation;
```

Set the current session isolation level

set session transaction isolation level repeatable read;

Set the current isolation level of the system

set global transaction isolation level repeatable read;

The default transaction isolation level of mysql is repeatable read, under normal circumstances, there are no special
requirements, and there is no need to modify it (because this level can meet the needs of most projects)

If you want to modify the default isolation level, you can modify it globally, modify my.inithe configuration file, and add at the end

#可选参数有:READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ,SERIALIZABLE.
[mysqld]
transaction-isolation = REPEATABLE-READ

mysql transaction ACID

acid properties of transactions

Atomicity (Atomicity)
Atomicity means that a transaction is an indivisible unit of work, and either all operations in a transaction occur or none occur.
Consistency (Consistency)
transaction must make the database change from one consistent state to another consistent state
Isolation (lsolation)
The isolation of transactions means that when multiple users access the database concurrently, the transactions opened by the database for each user cannot be disturbed by the operation data of other transactions, and multiple concurrent transactions must be isolated from each other.
Durability (Durability)
Persistence means that once a transaction is committed, its changes to the data in the database are permanent, and then even if the database fails, it should not have any impact on it.

mysql table type and storage engine

basic introduction

The table type of MySQL is determined by the storage engine (Storage Engines) , mainly including MylSAM, innoDB, Memory, etc.
MySQL data tables mainly support six types, namely: CSV.Memory, ARCHIVE.MRG
MYISAM, MYISAM, InnoBDB.
These six are divided into two categories

One type is "transaction-safe" that supports transactions, such as: InnoDB;
The rest belong to the second category, called "non-transaction-safe" (non-transaction-safe) does not support transactions [mysiam and memory].

Main storage engine/table type characteristics

Details

Focus on three types: MyISAM, InnoDB, MEMORY

MylSAM does not support transactions or foreign keys, but its access speed is fast and there is no requirement for transaction integrity
The InnoDB storage engine provides transaction safety with commit, rollback, and crash recovery capabilities. But compared to
the MylSAM storage engine, InnoDB writes are less efficient and take up more disk space to retain data and indexes.
The MEMORY storage engine uses in-memory content to create tables. Each MEMORY table actually only corresponds to
disk files. Table access of MEMORY type is very fast, because its data is placed in memory, and the HASH index is used by default. But once the MySQL service is closed, the data in the table will be lost , and the structure of the table is still there.

Three Storage Engine Table Use Cases

-- 表类型和存储引擎

-- 查看所有的存储引擎
SHOW ENGINES
-- innodb 存储引擎，是前面使用过.
-- 1. 支持事务 2. 支持外键 3. 支持行级锁

-- myisam 存储引擎
CREATE TABLE t28 (
	id INT,
	`name` VARCHAR(32)) ENGINE MYISAM
-- 1. 添加速度快 2. 不支持外键和事务 3. 支持表级锁

START TRANSACTION;
SAVEPOINT t1
INSERT INTO t28 VALUES(1, 'jack');
SELECT * FROM t28;
ROLLBACK TO t1

-- memory 存储引擎
-- 1. 数据存储在内存中[关闭了Mysql服务，数据丢失, 但是表结构还在] 
-- 2. 执行速度很快(没有IO读写) 3. 默认支持索引(hash表)

CREATE TABLE t29 (
	id INT,
	`name` VARCHAR(32)) ENGINE MEMORY
DESC t29 -- 表结构还在
INSERT INTO t29
	VALUES(1,'tom'), (2,'jack'), (3, 'hsp');
SELECT * FROM t29

-- 指令修改存储引擎
ALTER TABLE `t29` ENGINE = INNODB

How to choose a storage engine for a table

If your application does not need transactions and only handles basic CRUD operations, then MylSAM
is the best choice, and the speed is fast
If you need to support transactions, choose lnnoDB.
The Memory storage engine is to store data in the memory. Since there is no waiting for disk I/O, the speed is extremely fast. But because it is an in-memory storage engine, any modifications made will disappear after the server restarts. (classic usage user's online status()

Modify the storage engine

ALTER TABLE `表名` ENGINE = 储存引擎;

View (view)

look at a demand

There are a lot of column information in the emp table, some of which are important personal information (such as sal, comm, mgr, hiredate), if we want a user to only query the information of the emp table (empno, ename, job and deptno), what can be done ?=>View

basic concept

A view is a virtual table whose contents are defined by a query. Like real tables, views contain columns whose data comes from corresponding real tables (base tables)
Schematic diagram of the relationship between views and base tables:

Basic use of views

create view view name as select statement
alter view view name as select statement -- update to a new view
SHOW CREATE VIEW view name
drop view view name 1, view name 2

-- 视图的使用
-- 创建一个视图emp_view01，只能查询emp表的(empno、ename, job 和 deptno ) 信息

-- 创建视图
CREATE VIEW emp_view01
	AS
	SELECT empno, ename, job, deptno FROM emp; 

-- 查看视图
DESC emp_view01

SELECT * FROM emp_view01;
SELECT empno, job  FROM emp_view01;

-- 查看创建视图的指令
SHOW CREATE VIEW emp_view01
-- 删除视图
DROP VIEW emp_view01;


-- 视图的细节

-- 1. 创建视图后，到数据库去看，对应视图只有一个视图结构文件(形式: 视图名.frm) 
-- 2. 视图的数据变化会影响到基表，基表的数据变化也会影响到视图[insert update delete ]

-- 修改视图 会影响到基表

UPDATE emp_view01 
	SET job = 'MANAGER' 
	WHERE empno = 7369
	
SELECT * FROM emp; -- 查询基表


SELECT * FROM emp_view01

-- 修改基本表， 会影响到视图

UPDATE emp 
	SET job = 'SALESMAN' 
	WHERE empno = 7369

-- 3. 视图中可以再使用视图 , 比如从emp_view01 视图中，选出empno,和ename做出新视图
DESC emp_view01

CREATE VIEW emp_view02
	AS
	SELECT empno, ename FROM emp_view01
	
SELECT * FROM emp_view02

View Details Discussion

After creating the view, go to the database to see that there is only one view structure file for the corresponding view (form: view name.frm)
The data change of the view will affect the base table, and the data change of the base table will also affect the view [insert update delete]
A view can be reused in a view, and the data still comes from the base table.

View Best Practices

Safety. Some data sheets have important information. Some fields are confidential and cannot be seen directly by the user. At this time, you can create a view in which only a part of the fields are reserved. In this way, users can query the fields they need, but cannot view confidential fields.
performance. Data in a relational database is often stored in tables, and foreign keys are used to establish relationships between these tables. At this time, database queries usually use connections ( JOIN ). This is not only troublesome, but also relatively inefficient. If you create a view that combines related tables and fields, you can avoid using JOIN to query data.
flexible. If there is an old table in the system, this table will be discarded due to design problems. However, many applications are based on this table and cannot be easily modified. At this time, a view can be created, and the data in the view is directly mapped to the newly created table. In this way, a lot of changes can be made less, and the purpose of upgrading the data table is also achieved.

View classroom exercises

-- 视图的课堂练习
-- 针对 emp，dept , 和 salgrade 张三表.创建一个视图 emp_view03，
-- 可以显示雇员编号，雇员名，雇员部门名称和 薪水级别[即使用三张表，构建一个视图]
/*
	分析: 使用三表联合查询，得到结果
	将得到的结果，构建成视图
*/
CREATE VIEW emp_view03
	AS
	SELECT empno, ename, dname, grade
	FROM emp, dept, salgrade
	WHERE emp.deptno = dept.deptno AND 
	(sal BETWEEN losal AND hisal) 

DESC emp_view03
SELECT * FROM emp_view03

Mysql management

Mysql user

Users in mysql are stored in tables mysqlinuser the database

Among them, the important fields of the user table are explained as follows:

host: The "location" that is allowed to log in, localhost means that the user is only allowed to log in locally, or you can specify an ip address, for example: 192.168.1.100
user: username;
authentication string: password, which is encrypted by the password() function of mysql
.

create user

create user '用户名'@'允许登录位置' identified by '密码'

Description: Create a user and specify a password at the same time

delete users

drop user '用户名'@'允许登录位置';

user change password

Modify your own password:

set password = password('密码');

Modify other people's passwords (requires permission to modify user passwords):

set password for '用户名'@'登录位置'=password('密码');

Privileges in mysql

Authorize the user

Basic syntax:

grant 权限列表 on 库.对象名 to '用户名'@'登录位置'【identified  by '密码'】

illustrate:

Permission list, multiple permissions are separated by commas

grant select on …

grant select,delete,create on …

grant all [privileges] on … //Indicates that the user is granted all permissions on the object
Special Note
*.*: Represents all objects (tables, views, stored procedures) of all databases in this system

库.*: Represents all data objects (tables, views, stored procedures, etc.) in a database
identified by can be omitted or written out.

(1) If the user exists, it is to modify the password of the user at the same time.

(2) If the user does not exist, create the user!

Recycle User Authorization

Basic syntax:

revoke 权限列表 on 库.对象名 from '用户名'@'登录位置';

Authorization Validation Command

If the permission does not take effect, you can execute the following command, the basic syntax:

FLUSH PRIVILEGES;

-- Mysql用户的管理
-- 原因：当我们做项目开发时，可以根据不同的开发人员，赋给他相应的Mysql操作权限
-- 所以，Mysql数据库管理人员(root), 根据需要创建不同的用户，赋给相应的权限，供人员使用

-- 1. 创建新的用户
-- 解读 (1) 'hsp_edu'@'localhost' 表示用户的完整信息 'hsp_edu' 用户名 'localhost' 登录的IP
-- (2) 123456 密码, 但是注意 存放到 mysql.user表时，是password('123456') 加密后的密码
--     *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9
CREATE USER 'hsp_edu'@'localhost' IDENTIFIED BY '123456'

SELECT `host`, `user`, authentication_string  
	FROM mysql.user

-- 2. 删除用户
DROP USER 'hsp_edu'@'localhost'

-- 3. 登录

-- root 用户修改 hsp_edu@localhost 密码, 是可以成功.
SET PASSWORD FOR 'hsp_edu'@'localhost' = PASSWORD('123456')

classroom exercises

User Management Exercises

Create a user (your name, pinyin), password 123, and can only log in locally, not allowing remote login to mysql
Create the news table under the library and table testdb, requirement: use root user to create
Assign users permission to view the news table and add data
Test to see if the user has only these permissions
Change the password to abc, requirement: use the root user to complete
re-register
Delete your user as root user

-- 演示 用户权限的管理

-- 创建用户 shunping  密码 123 , 从本地登录
CREATE USER 'shunping'@'localhost' IDENTIFIED BY '123'

-- 使用root 用户创建 testdb  ,表 news
CREATE DATABASE testdb
CREATE TABLE news (
	id INT ,
	content VARCHAR(32));
-- 添加一条测试数据
INSERT INTO news VALUES(100, '北京新闻');
SELECT * FROM news;

-- 给 shunping 分配查看 news 表和 添加news的权限
GRANT SELECT , INSERT 
	ON testdb.news
	TO 'shunping'@'localhost'
	
-- 可以增加update权限
GRANT UPDATE  
	ON testdb.news
	TO 'shunping'@'localhost'
	
	
-- 修改 shunping的密码为 abc
SET PASSWORD FOR 'shunping'@'localhost' = PASSWORD('abc');

-- 回收 shunping 用户在 testdb.news 表的所有权限
REVOKE SELECT , UPDATE, INSERT ON testdb.news FROM 'shunping'@'localhost'
REVOKE ALL ON testdb.news FROM 'shunping'@'localhost'

-- 删除 shunping
DROP USER 'shunping'@'localhost'

Details

When creating a user, if the Host is not specified, it will be %, % means that all IPs have connection permissions
```
create user XX;
```
You can also specify
create user 'xxx'@'192.168.1.%' that the ip 192.168.1.*of can log in to mysql
When deleting a user, if the host is not %, you need to explicitly specify 'user'@'host value'

-- 说明 用户管理的细节
-- 在创建用户的时候，如果不指定Host, 则为% , %表示表示所有IP都有连接权限 
-- create user  xxx;

CREATE USER jack

SELECT `host`, `user` FROM mysql.user

-- 你也可以这样指定 
-- create user  'xxx'@'192.168.1.%'  表示 xxx用户在 192.168.1.*的ip可以登录mysql

CREATE USER 'smith'@'192.168.1.%'

-- 在删除用户的时候，如果 host 不是 %, 需要明确指定  '用户'@'host值'

DROP USER jack -- 默认就是 DROP USER 'jack'@'%'

DROP USER 'smith'@'192.168.1.%'

Homework for this chapter

1. Multiple choice questions

(1). Which of the following statements is wrong? [D]

A.SELECT empno,ename name,sal salary FROM emp;
B.SELECT empno,ename name,sal AS salary FROM emp;
C.SELECT ename,sal*12 AS "Annual Salary" FROM emp;
D.SELECT ename,sal*12 Annual Salary FROM emp; -- 有空格最好引起来

(2). A user wants to display the information of all employees whose subsidy is not empty, which statement should be used? [B]

A.SELECT ename.sal,comm FROM emp WHERE comm<>null;
B.SELECT ename,sal,comm FROM emp WHERE comm IS NOT null;
C.SELECT ename,sal,comm FROM emp WHERE comm<>0;

(3). Which of the following statements is wrong? [C]

A.SELECT ename,sal salary FROM emp ORDER BY sal;
B.SELECT ename,sal salary FROM emp ORDER BY salary；
C. SELECT ename,sal salary FROM emp ORDER BY 3;

2. Write the sql statement to view the structure of DEPT table and EMP table

-- 2. 写出 查看DEPT表和EMP表的结构 的sql语句
-- 
	DESC dept
	DESC emp

3. Use a simple query statement to complete:

(1) Display all department names.

(2) Display all employee names and their annual income 13 months (salary + subsidies), and specify the column alias "annual income"

-- 3. 使用简单查询语句完成:
-- (1) 显示所有部门名称。
SELECT dname 
	FROM dept;
-- (2) 显示所有雇员名及其全年收入 13月(工资+补助),并指定列别名"年收入"
SELECT ename, (sal + IFNULL(comm,0)) * 13 AS "年收入"
	FROM emp 
SELECT * FROM emp;

4. Restrict query data.
(1) Display the name and salary of employees whose salary is more than 2850.

(2) Display the name and salary of all employees whose salary is not between 1500 and 2850.

(3) Display the name and department number of the employee numbered 7566.

(4) Display the names and salaries of employees whose salaries exceed 1500 in departments 10 and 30.

(5) Display the names and positions of employees without managers.

-- 4.限制查询数据。
-- (1) 显示工资超过2850的雇员姓名和工资。
SELECT ename, sal
	FROM emp 
	WHERE sal > 2850
-- (2) 显示工资不在1500到2850之间的所有雇员名及工资。
SELECT ename, sal
	FROM emp 
	WHERE sal < 1500 OR sal > 2850
	
SELECT ename, sal
	FROM emp 
	WHERE NOT (sal >= 1500 AND sal <= 2850)
-- (3) 显示编号为7566的雇员姓名及所在部门编号。
SELECT ename, deptno
	FROM emp 
	WHERE empno = 7566
-- (4) 显示部门10和30中工资超过1500的雇员名及工资。
SELECT ename, job
	FROM emp 
	WHERE (deptno = 10 OR deptno = 30) AND sal > 1500
-- (5) 显示无管理者的雇员名及岗位。
SELECT ename, job 
	FROM emp
	WHERE mgr IS NULL;

5. Sort the data.

1) Display the name, position and employment date of the employees hired between February 1, 1991 and May 1, 1991, and sort by the employment date [default].

2) Display the names, wages and subsidies of all employees receiving subsidies, and sort them in descending order of wages

-- 5.排序数据。
-- (1) 显示在1991年2月1日到1991年5月1日之间雇用的雇员名,岗位及雇佣日期, 
-- 并以雇佣日期进行排序[默认]。
-- 思路 1. 先查询到对应结果 2. 考虑排序
SELECT ename, job, hiredate
	FROM emp
	WHERE hiredate >= '1991-02-01' AND hiredate <= '1991-05-01'
	ORDER BY hiredate

-- (2) 显示获得补助的所有雇员名,工资及补助,并以工资降序排序
SELECT ename, sal, comm
	FROM emp
	ORDER BY sal DESC

6. According to: emp employee table write correct SQL

–1. Select all employees in department 30.

–2. List the name, number and department number of all clerks (CLERK)

–3. Find employees whose commission is higher than their salary.

–4. Find employees whose commission is higher than 60% of salary.

–5. Find out the details of all managers (MANAGER) in department 10 and all clerks (CLERK) in department 20.

–6. Find the details of all managers (MANAGER) in department 10, all clerks (CLERK) in department 20, and all employees who are neither managers nor clerks but whose salary is greater than or equal to 2000.

–7. Find out the different jobs of the employees who receive commissions.

–8. Find out the employees who don’t charge commissions or charge less than 100 commissions. –9. Find all the employees who are employed on the third last day of each month.

–10. Find employees who were hired earlier than 12 years ago.

–11. Display the names of all employees in lowercase.

–12.Displays the names of employees with exactly 5 characters.

–13. Display the names of employees without "R".

–14. Display the first three characters of all employee names.

–15. Display the names of all employees, replacing all "A" with a

–16. Show the names and dates of employment of employees who have completed 10 years of service.

–17. Display employee details, sorted by name.

–18. Display the employee’s name and date of employment, sorting the oldest employee first based on their years of service.

–19. Display the name, job and salary of all employees, sort by job in descending order, and sort by salary if the job is the same.

–20. Display the names of all employees, the year and month when they joined the company, and sort by the month of the employment date. If the month is the same, the employee with the earliest year will be ranked first.

–21. Display the daily salary of all employees in a month with 30 days, ignoring the remainder.

–22. Find all employees who were hired in February (of any year).

–23. For each employee, display the number of days he joined the company.

–24.Display the names of all employees whose name field contains "A" anywhere.

–25. Display the service years of all employees in the form of year, month and day. (probably)

-- homework03

-- ------1.选择部门30中的所有员工.
SELECT * FROM 
	emp
	WHERE deptno = 30
-- ------2.列出所有办事员(CLERK)的姓名，编号和部门编号. 
SELECT ename, empno, deptno, job FROM 
	emp
	WHERE job = 'CLERK'
-- ------3.找出佣金高于薪金的员工.
SELECT * FROM 
	emp
	WHERE IFNULL(comm, 0) > sal
-- ------4.找出佣金高于薪金60%的员工.
SELECT * FROM 
	emp
	WHERE IFNULL(comm, 0) > sal * 0.6
-- ------5.找出部门10中所有经理(MANAGER)和部门20中所有办事员(CLERK)的详细资料.
-- 
SELECT * FROM
	emp
	WHERE (deptno = 10 AND job = 'MANAGER') 
	OR (deptno = 20 AND job = 'CLERK')
-- ------6.找出部门10中所有经理(MANAGER),部门20中所有办事员(CLERK), 
 -- 还有既不是经理又不是办事员但其薪金大于或等于2000的所有员工的详细资料.
SELECT * FROM
	emp
	WHERE (deptno = 10 AND job = 'MANAGER') 
	OR (deptno = 20 AND job = 'CLERK')
	OR (job != 'MANAGER' AND job != 'CLERK' AND sal >= 2000 )
-- ------7.找出收取佣金的员工的不同工作.
SELECT DISTINCT job
	FROM emp
	WHERE comm IS NOT NULL

-- ------8.找出不收取佣金或收取的佣金低于100的员工.
SELECT *
	FROM emp
	WHERE comm IS  NULL OR IFNULL(comm, 0) < 100
-- ------9.找出各月倒数第3天受雇的所有员工.
-- 提示: last_day(日期)， 可以返回该日期所在月份的最后一天
-- last_day(日期) - 2 得到日期所有月份的倒数第3天
SELECT * 
	FROM emp
	WHERE LAST_DAY(hiredate) - 2  =  hiredate

-- ------10.找出早于12年前受雇的员工.（即 入职时间超过12年）
SELECT * 
	FROM emp
	WHERE DATE_ADD(hiredate, INTERVAL 12 YEAR) < NOW() 

-- 
-- ------11.以首字母小写的方式显示所有员工的姓名.
SELECT CONCAT(LCASE(SUBSTRING(ename,1,1)), SUBSTRING(ename,2))
	FROM emp;
-- ------12.显示正好为5个字符的员工的姓名.

SELECT * 
	FROM emp
	WHERE LENGTH(ename) = 5

-- ------13.显示不带有"R"的员工的姓名.
SELECT * 
	FROM emp
	WHERE ename NOT LIKE '%R%'
-- ------14.显示所有员工姓名的前三个字符.
SELECT LEFT(ename,3)
	FROM emp
-- ------15.显示所有员工的姓名,用a替换所有"A"
SELECT REPLACE(ename, 'A', 'a') 
	FROM emp
-- ------16.显示满10年服务年限的员工的姓名和受雇日期.
SELECT ename, hiredate
	FROM emp
	WHERE DATE_ADD(hiredate, INTERVAL 10 YEAR) <= NOW()
-- ------17.显示员工的详细资料,按姓名排序.

-- ------18.显示员工的姓名和受雇日期,根据其服务年限,将最老的员工排在最前面.
-- 
SELECT ename, hiredate
	FROM emp
	ORDER BY hiredate 
-- ------19.显示所有员工的姓名、工作和薪金,按工作降序排序,若工作相同则按薪金排序.
SELECT ename, job, sal
	FROM emp
	ORDER BY job DESC, sal 
-- ------20.显示所有员工的姓名、加入公司的年份和月份,按受雇日期所在月排序,
-- 若月份相同则将最早年份的员工排在最前面.
SELECT ename, CONCAT(YEAR(hiredate),'-', MONTH(hiredate))
	FROM emp
	ORDER BY MONTH(hiredate), YEAR(hiredate)

-- ------21.显示在一个月为30天的情况所有员工的日薪金,忽略余数.
SELECT ename, FLOOR(sal / 30), sal / 30 
	FROM emp; 
-- ------22.找出在(任何年份的)2月受聘的所有员工。
SELECT * 
	FROM emp
	WHERE MONTH(hiredate) = 2
-- ------23.对于每个员工,显示其加入公司的天数.
-- 
SELECT ename, DATEDIFF(NOW(), hiredate) 
	FROM emp
-- ------24.显示姓名字段的任何位置包含"A"的所有员工的姓名.
SELECT *
	FROM emp
	WHERE ename LIKE '%A%'
-- ------25.以年月日的方式显示所有员工的服务年限.   (大概)

-- 思路 1. 先求出 工作了多少天 
SELECT ename, FLOOR(DATEDIFF(NOW(), hiredate) / 365) AS " 工作年 ", 
	FLOOR((DATEDIFF(NOW(), hiredate) % 365) / 31) AS " 工作月 ",
	DATEDIFF(NOW(), hiredate) % 31 AS " 工作天"
	FROM emp;

7. According to: emp employee table, dept department table, salary = salary sal + commission comm, write the correct SQL

(1) List all departments that have at least one employee

(2) List all employees whose salary is more than "SMITH".

(3) List all employees whose employment date is later than their immediate supervisor.

(4) List the names of departments and the employee information of these departments, and list those departments without employees

(5) List the names of all "CLERK" (clerks) and their department names.

(6) List various jobs with a minimum salary greater than 1500.

(7) List the names of the employees who work in the department "SALES" (sales department).

(8) List all employees whose salary is higher than the company's average salary.

(9) List all employees who do the same job as "SCOTT".

(10) List the names and salaries of employees whose salaries are higher than those of all employees working in department 30

(11) List the number of employees working in each department, the average salary, and the average length of service.

(12) List the names, department names, and salaries of all employees.

(13) List the detailed information and the number of people in all departments.

(14) List minimum wages for various jobs.

(15) List the minimum salary of MANAGER (manager).

(16) List the annual salary of all employees, sorted by annual salary from low to high.

-- 
-- (1)．列出至少有一个员工的所有部门

/*
	先查出各个部门有多少人
	使用 having 子句过滤
*/
SELECT COUNT(*) AS c, deptno
	FROM emp 
	GROUP BY deptno 
	HAVING c > 1
-- (2)．列出薪金比“SMITH”多的所有员工。
/*
	先查出 smith 的 sal => 作为子查询
	然后其他员工 sal 大于 smith 即可
*/
SELECT * 
	FROM emp
	WHERE sal > (
		SELECT sal 
			FROM emp 
			WHERE ename = 'SMITH'
	)
-- (3)．列出受雇日期晚于其直接上级的所有员工。
/*
	先把 emp 表 当做两张表 worker , leader
	条件 1. worker.hiredate > leader.hiredate
	     2. worker.mgr = leader.empno
*/

SELECT worker.ename AS '员工名', worker.hiredate AS '员工入职时间',
	leader.ename  AS '上级名', leader.hiredate AS '上级入职时间' 
	FROM emp worker , emp leader
	WHERE worker.hiredate > leader.hiredate 
	AND worker.mgr = leader.empno;

-- (4)．列出部门名称和这些部门的员工信息，同时列出那些没有员工的部门。

/*
	这里因为需要显示所有部门，因此考虑使用外连接，(左外连接)
	如果没有印象了，去看看老师讲的外连接.
*/
SELECT dname, emp.*
	FROM dept 
	LEFT JOIN emp ON dept.deptno = emp.deptno 

-- (5)．列出所有“CLERK”（办事员）的姓名及其部门名称。

SELECT ename, dname , job
	FROM emp, dept
	WHERE job = 'CLERK' AND emp.deptno = dept.deptno

-- (6)．列出最低薪金大于1500的各种工作。

/*
	查询各个部门的最低工资
	使用having 子句进行过滤
*/
SELECT MIN(sal) AS min_sal , job
	FROM emp
	GROUP BY job
	HAVING min_sal > 1500
-- (7)．列出在部门“SALES”（销售部）工作的员工的姓名。

SELECT ename, dname
	FROM emp , dept
	WHERE emp.deptno = dept.deptno AND dname = 'SALES'

-- (8)．列出薪金高于公司平均薪金的所有员工。

SELECT *
	FROM emp
	WHERE sal > (
		SELECT AVG(sal) 
			FROM emp
	)

-- (9)．列出与“SCOTT”从事相同工作的所有员工。

SELECT * 
	FROM emp
	WHERE job = (
		SELECT job 
			FROM emp
			WHERE ename = 'SCOTT'
	) AND ename != 'SCOTT'

-- (10)．列出薪金高于所在部门30的工作的所有员工的薪金的员工姓名和薪金。


-- 先查询出30部门的最高工资
SELECT ename, sal 
	FROM emp 
	WHERE sal > (
		SELECT MAX(sal) 
			FROM emp
			WHERE deptno = 30
	) 
-- (11)．列出在每个部门工作的员工数量、平均工资和平均服务期限(时间单位)。
-- 老师建议 ， 写sql 也是一步一步完成的
SELECT COUNT(*) AS "部门员工数量", deptno , AVG(sal) AS "部门平均工资" , 
	FORMAT(AVG(DATEDIFF(NOW(), hiredate) / 365 ),2) AS " 平均服务期限(年)"
	FROM emp 
	GROUP BY deptno

-- (12)．列出所有员工的姓名、部门名称和工资。

-- 就是 emp 和 dept 联合查询 ，连接条件就是 emp.deptno = dept.deptno

-- (13)．列出所有部门的详细信息和部门人数。

-- 1. 先得到各个部门人数 , 把下面的结果看成临时表 和 dept表联合查询
SELECT COUNT(*) AS c , deptno 
	FROM emp
	GROUP BY deptno

-- 2. 
SELECT dept.*, tmp.c AS "部门人数"
	FROM dept, (
		SELECT COUNT(*) AS c , deptno 
		FROM emp
		GROUP BY deptno
	) tmp 
	WHERE dept.deptno = tmp.deptno

-- (14)．列出各种工作的最低工资。

SELECT MIN(sal), job
	FROM emp
	GROUP BY job
-- (15)．列出MANAGER（经理）的最低薪金。

SELECT MIN(sal), job
	FROM emp
	WHERE job = 'MANAGER'
-- (16)．列出所有员工的年工资,按年薪从低到高排序。

-- 1. 先得到员工的年工资
SELECT ename, (sal + IFNULL(comm, 0)) * 12 year_sal
	FROM emp
	ORDER BY year_sal

8. The school environment is set as follows: a department has several majors, each major only recruits one class a year, and each class has several students. Now it is necessary to establish a database about the department, students, and classes. The relationship model is:

Class CLASS (class number classid, major name subject, department name deptname, enrollment year enrollmenttime, number of people num)
Student STUDENT (student number studentid, name name, age age, class number classid)
Department DEPARTMENT (department number departmentid, department name deptname)

Use the SQL language to complete the following functions:

(1) To build a table, it is required to declare in the definition:
(1) The primary foreign code of each table.

(2) deptname is the only constraint.

(3) Student name cannot be empty.

(2) Insert the following data

DEPARTMENT (001, Mathematics; 002, Computer; 003, Chemistry; 004, Chinese; 005, Economics;)

(3) Complete the following query functions

3.1 Find out all students surnamed Li.

3.2 List the names of all departments offering more than one major

3.3 List the numbers and names of the departments with more than or equal to 30 people.

(4) The school added a new physics department, numbered 006

(5) Student Zhang San withdraws from school, please update the relevant form

-- 完成最后一个综合的练习

-- 8. 设学校环境如下:一个系有若干个专业，每个专业一年只招一个班，每个班有若干个学生。
-- 现要建立关于系、学生、班级的数据库，关系模式为：
-- 班CLASS （班号classid，专业名subject，系名deptname，入学年份enrolltime，人数num）
-- 学生STUDENT （学号studentid，姓名name，年龄age，班号classid）
-- 系 DEPARTMENT （系号departmentid，系名deptname）
-- 试用SQL语言完成以下功能：  homework05.sql 10min 
-- 
-- (1) 建表，在定义中要求声明：
--     （1）每个表的主外码。
--     （2）deptname是唯一约束。
--     （3）学生姓名不能为空。

-- 创建表 系 DEPARTMENT （系号departmentid，系名deptname）
CREATE TABLE DEPARTMENT (
	departmentid VARCHAR(32) PRIMARY KEY,
	deptname VARCHAR(32) UNIQUE NOT NULL);
	
-- 班CLASS （班号classid，专业名subject，系名deptname，入学年份enrolltime，人数num）
CREATE TABLE `class` (
	classid INT PRIMARY KEY,
	`subject` VARCHAR(32) NOT NULL DEFAULT '',
	deptname VARCHAR(32) , -- 外键字段，在表定义后指定
	enrolltime INT NOT NULL DEFAULT 2000,
	num INT NOT NULL DEFAULT 0,
	FOREIGN KEY (deptname) REFERENCES  DEPARTMENT(deptname));
	
-- 学生STUDENT （学号studentid，姓名name，年龄age，班号classid）
CREATE TABLE hsp_student (
	studentid INT PRIMARY KEY,
	`name` VARCHAR(32) NOT NULL DEFAULT '',
	age INT NOT NULL DEFAULT 0,
	classid INT, -- 外键
	FOREIGN KEY (classid) REFERENCES  `class`(classid));
	
-- 添加测试数据

INSERT INTO department VALUES('001','数学');
INSERT INTO department VALUES('002','计算机');
INSERT INTO department VALUES('003','化学');
INSERT INTO department VALUES('004','中文');
INSERT INTO department VALUES('005','经济');

INSERT INTO class VALUES(101,'软件','计算机',1995,20);
INSERT INTO class VALUES(102,'微电子','计算机',1996,30);
INSERT INTO class VALUES(111,'无机化学','化学',1995,29);
INSERT INTO class VALUES(112,'高分子化学','化学',1996,25);
INSERT INTO class VALUES(121,'统计数学','数学',1995,20);
INSERT INTO class VALUES(131,'现代语言','中文',1996,20);
INSERT INTO class VALUES(141,'国际贸易','经济',1997,30);
INSERT INTO class VALUES(142,'国际金融','经济',1996,14);

INSERT INTO hsp_student VALUES(8101,'张三',18,101);
INSERT INTO hsp_student VALUES(8102,'钱四',16,121);
INSERT INTO hsp_student VALUES(8103,'王玲',17,131);
INSERT INTO hsp_student VALUES(8105,'李飞',19,102);
INSERT INTO hsp_student VALUES(8109,'赵四',18,141);
INSERT INTO hsp_student VALUES(8110,'李可',20,142);
INSERT INTO hsp_student VALUES(8201,'张飞',18,111);
INSERT INTO hsp_student VALUES(8302,'周瑜',16,112);
INSERT INTO hsp_student VALUES(8203,'王亮',17,111);
INSERT INTO hsp_student VALUES(8305,'董庆',19,102);
INSERT INTO hsp_student VALUES(8409,'赵龙',18,101);

SELECT * FROM department
SELECT * FROM class
SELECT * FROM hsp_student

-- (3) 完成以下查询功能
--   3.1 找出所有姓李的学生。
-- 查表 hsp_student , like
SELECT * 
	FROM hsp_student
	WHERE `name` LIKE '李%' 
--   3.2 列出所有开设超过1个专业的系的名字。

-- 1. 先查询各个系有多少个专业
SELECT COUNT(*) AS nums, deptname 
	FROM class
	GROUP BY deptname HAVING nums > 1
--   3.3 列出人数大于等于30的系的编号和名字。
-- 1. 先查出各个系有多少人, 并得到 >= 30 的系

SELECT SUM(num) AS nums, deptname  
	FROM class 
	GROUP BY  deptname 
	HAVING nums >= 30
	
-- 2. 将上面的结果看成一个临时表 和 department 联合查询即可

SELECT  tmp.*, department.departmentid
	FROM department , (
		SELECT SUM(num) AS nums, deptname  
		FROM class 
		GROUP BY  deptname 
		HAVING nums >= 30
	) tmp 
	WHERE department.deptname = tmp.deptname;
	


-- (4) 学校又新增加了一个物理系，编号为006
-- 添加一条数据
INSERT INTO department VALUES('006','物理系');
-- (5) 学生张三退学，请更新相关的表

-- 分析：1. 张三所在班级的人数-1 2. 将张三从学生表删除  3. 需要使用事务控制

-- 开启事务
START TRANSACTION;
-- 张三所在班级的人数-1 
UPDATE class SET num = num - 1
	WHERE classid = (
		SELECT classid 
			FROM hsp_student 
			WHERE NAME = '张三'
	);

DELETE 
	FROM hsp_student
	WHERE NAME = '张三';
	
-- 提交事务
COMMIT;

SELECT * FROM hsp_student;
SELECT * FROM class

The necessary knowledge for getting started with MySQL supplemented by Java

Article Directory

Zero-based learning MySQL

solution

file, database

MySQL database installation and configuration

Use the command line window to connect to the MYSQL database

Operation Diagram

Three-tier database structure

How data is stored in the database

Classification of SQL statements

create database

View, delete database

backup restore database

Backup and restore database tables

create table

Mysql common data types (column types)

Basic use of numeric (integer)

define an unsigned integer

Use of numeric type (bit)

Basic use of numeric (decimal)

Basic use of strings

String Usage Details

Basic use of date types

Create table exercise

Modify Table - Basic Introduction

Modification Sheet - Class Exercise

Database C[create]R[read]U[update]D[delete] statement

Insert statement

Insert data into a table using the INSERT statement.

Details

update statement

Use the update statement to modify the data in the table

basic use

usage details

delete statement

Use the delete statement to delete data in the table

usage details

select statement

basic grammar

Notes (create test table student table)

practise

Use expressions to operate on the columns of the query

The as statement can be used in the select statement

practise

Operators frequently used in where clauses

Use where clause to filter queries

Use the order by clause to sort query results

Aggregation/statistical functions

count

sum

avg

max/min

Group columns using the group by clause

Use the having clause to filter the grouped results

String related functions

math related functions

Date and time related functions

Encryption and System Functions

flow control function

mysql table query – enhanced

introduce

Paging query

Using grouping functions and grouping clauses

Summary of Data Grouping

mysql multi-table query

Multi-table query practice

self-join

mysql table subquery

what is a subquery

single row subquery

multi-row subquery

Subqueries are used as temporary tables

Using the all operator in a multi-row subquery

Using the any operator in a multi-row subquery

multi-column subquery

Using a subquery in the from clause

table replication

Self-replicating data (worm replication)

combined query