这篇博客详细介绍了MySQL的基础知识，包括关系型数据库的概念、MySQL的安装配置、数据库组件、SQL语句的三大类别（DDL、DML、DCL）以及数据类型。此外，还涵盖了MySQL数据库的创建、表操作、用户管理、查询和授权等实战操作。
目录
1. 关系型数据库介绍
1.1 数据结构模型
数据结构模型主要有：
- 层次模型
- 网状结构
- 关系模型
关系模型：
二维关系：row，column
数据库管理系统：DBMS
关系：Relational，RDBMS
1.2 RDBMS专业名词
常见的关系型数据库管理系统：
- MySQL：MySQL，MariaDB，Percona-Server
- PostgreSQL：简称为pgsql
- Oracle
- MSSQL
SQL：Structure Query Language，结构化查询语言
约束：constraint，向数据表提供的数据要遵守的限制
- 主键约束：一个或多个字段的组合，填入的数据必须能在本表中唯一标识本行。且必须提供数据，不能为空（NOT NULL）。
-
- 一个表只能存在一个
- 惟一键约束：一个或多个字段的组合，填入的数据必须能在本表中唯一标识本行。允许为空（NULL）
-
- 一个表可以存在多个
- 外键约束：一个表中的某字段可填入数据取决于另一个表的主键已有的数据
- 检查性约束
索引：将表中的一个或多个字段中的数据复制一份另存，并且这些数据需要按特定次序排序存储
1.3 关系型数据库的常见组件
关系型数据库的常见组件有：
- 数据库：database
- 表：table，由行（row）和列（column）组成
- 索引：index
- 视图：view
- 用户：user
- 权限：privilege
- 存储过程：procedure
- 存储函数：function
- 触发器：trigger
- 事件调度器：event scheduler
1.4 SQL语句
SQL语句有三种类型：
- DDL：Data Defination Language，数据定义语言
- DML：Data Manipulation Language，数据操纵语言
- DCL：Data Control Language，数据控制语言
| SQL语句类型 | 对应操作 |
| DDL | CREATE：创建 |
| DML | INSERT：向表中插入数据 |
| DCL | GRANT：授权 |
1.5 数据类型
MySQL中定义数据字段的类型对数据库的优化是非常重要的。MySQL支持多种类型，大致可以分为三类：数值、日期/时间和字符串(字符)类型。
数值类型
MySQL支持所有标准SQL数值数据类型。这些类型包括严格数值数据类型(INTEGER、SMALLINT、DECIMAL和NUMERIC)，以及近似数值数据类型(FLOAT、REAL和DOUBLE PRECISION)。
关键字INT是INTEGER的同义词，关键字DEC是DECIMAL的同义词。BIT数据类型保存位字段值，并且支持MyISAM、MEMORY、InnoDB和BDB表。作为SQL标准的扩展，MySQL也支持整数类型TINYINT、MEDIUMINT和BIGINT。下面的表显示了需要的每个整数类型的存储和范围
| 类型 | 大小 | 范围（有符号） | 范围（无符号） | 用途 |
| TINYINT | 1 byte | (-128，127) | (0，255) | 小整数值 |
| SMALLINT | 2 bytes | (-32 768，32 767) | (0，65 535) | 大整数值 |
| MEDIUMINT | 3 bytes | (-8 388 608，8 388 607) | (0，16 777 215) | 大整数值 |
| INT或INTEGER | 4 bytes | (-2 147 483 648，2 147 483 647) | (0，4 294 967 295) | 大整数值 |
| BIGINT | 8 bytes | (-9,223,372,036,854,775,808，9 223 372 036 854 775 807) | (0，18 446 744 073 709 551 615) | 极大整数值 |
| FLOAT | 4 bytes | (-3.402 823 466 E+38，-1.175 494 351 E-38)，0，(1.175 494 351 E-38，3.402 823 466 351 E+38) | 0，(1.175 494 351 E-38，3.402 823 466 E+38) | 单精度 |
| DOUBLE | 8 bytes | (-1.797 693 134 862 315 7 E+308，-2.225 073 858 507 201 4 E-308)，0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308) | 0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308) | 双精度 |
| DECIMAL | 对DECIMAL(M,D) ，如果M>D，为M+2否则为D+2 | 依赖于M和D的值 | 依赖于M和D的值 | 小数值 |
时间类型：
| 类型 | 大小( bytes) | 范围 | 格式 | 用途 |
| DATE | 3 | 1000-01-01/9999-12-31 | YYYY-MM-DD | 日期值 |
| TIME | 3 | '-838:59:59'/'838:59:59' | HH:MM:SS | 时间值或持续时间 |
| YEAR | 1 | 1901/2155 | YYYY | 年份值 |
| DATETIME | 8 | 1000-01-01 00:00:00/9999-12-31 23:59:59 | YYYY-MM-DD HH:MM:SS | 混合日期和时间值 |
| TIMESTAMP | 4 | 1970-01-01 00:00:00/2038 结束时间是第 2147483647 秒，北京时间 2038-1-19 11:14:07，格林尼治时间 2038年1月19日 凌晨 03:14:07 | YYYYMMDD HHMMSS | 混合日期和时间值，时间戳 |
字符串类型：
| 类型 | 大小 | 用途 |
| CHAR | 0-255 bytes | 定长字符串 |
| VARCHAR | 0-65535 bytes | 变长字符串 |
| TINYBLOB | 0-255 bytes | 不超过 255 个字符的二进制字符串 |
| TINYTEXT | 0-255 bytes | 短文本字符串 |
| BLOB | 0-65 535 bytes | 二进制形式的长文本数据 |
| TEXT | 0-65 535 bytes | 长文本数据 |
| MEDIUMBLOB | 0-16 777 215 bytes | 二进制形式的中等长度文本数据 |
| MEDIUMTEXT | 0-16 777 215 bytes | 中等长度文本数据 |
| LONGBLOB | 0-4 294 967 295 bytes | 二进制形式的极大文本数据 |
| LONGTEXT | 0-4 294 967 295 bytes | 极大文本数据 |
2. mysql安装与配置
2.1 mysql安装
mysql安装方式有三种：
- 源代码：编译安装
- 二进制格式的程序包：展开至特定路径，并经过简单配置后即可使用
- 程序包管理器管理的程序包：
-
- rpm：有两种
-
-
- OS Vendor：操作系统发行商提供的
- 项目官方提供的
-
-
- deb
下载的方式：
//源码安装
//下载源码包
[root@Gin ~]# wget -O /usr/src/mysql57-community-release-el7-10.noarch.rpm http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm
mysql57-community-re 100%[===================>] 24.95K --.-KB/s in 0.1s
2022-07-25 16:13:09 (174 KB/s) - ‘mysql57-community-release-el7-10.noarch.rpm’ saved [25548/25548]
//安装MySQL源码包
[root@Gin ~]# rpm -Uvh mysql57-community-release-el7-10.noarch.rpm
warning: mysql57-community-release-el7-10.noarch.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY
Verifying... ################################# [100%]
Preparing... ################################# [100%]
Updating / installing...
1:mysql57-community-release-el7-10 ################################# [100%]
//禁用MySQL
[root@Gin ~]# yum module disable mysql
Repository extras is listed more than once in the configuration
Last metadata expiration check: 0:01:09 ago on Mon 25 Jul 2022 04:14:41 PM CST.
Module yaml error: Unexpected key in data: static_context [line 9 col 3]
Module yaml error: Unexpected key in data: static_context [line 9 col 3]
Dependencies resolved.
Nothing to do.
Complete!
//下载依赖包
yum -y install mysql-community-server mysql-community-client mysql-community-common mysql-community-devel --nogpgcheck
//yum安装
//下载mariadb包
yum install -y mariadb*
//设置开机自启
systemctl enable --now mariadb
//修改密码
mysql
set password = password('xxxx');
exit
//登录MySQL
mysql -uroot -pxxxx
2.2 mysql配置
//注意前一步安装时将MySQL禁用这里需要开启
[root@Gin ~]# service mysqld restart
Redirecting to /bin/systemctl restart mysqld.service
//启动mysql并设置开机自动启动
[root@Gin ~]# systemctl enable --now mysqld
[root@Gin ~]# systemctl status mysqld.service
● mysqld.service - MySQL Server
Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor prese>
Active: active (running) since Mon 2022-07-25 16:23:20 CST; 38s ago
Docs: man:mysqld(8)
http://dev.mysql.com/doc/refman/en/using-systemd.html
Main PID: 2537 (mysqld)
Tasks: 27 (limit: 23484)
Memory: 341.5M
CGroup: /system.slice/mysqld.service
└─2537 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld>
Jul 25 16:23:10 Gin systemd[1]: Starting MySQL Server...
Jul 25 16:23:20 Gin systemd[1]: Started MySQL Server.
//查看3306端口已经开启
[root@Gin ~]# ss -anltup | grep 3306
tcp LISTEN 0 80 *:3306 *:* users:(("mysqld",pid=2537,fd=22))
//在日志文件中找出临时密码
[root@Gin ~]# grep "password" /var/log/mysqld.log
2022-07-25T08:23:17.626555Z 1 [Note] A temporary password is generated for root@localhost: aCF=&Pq7uZtv
//使用获取到的临时密码登录mysql
[root@Gin ~]# mysql -uroot -p
Enter password: //在这里输入MySQL的临时密码
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.38
Copyright (c) 2000, 2022, Oracle and/or its affiliates.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> //看到mysql> 就表示已经成功进入MySQL
//修改mysql登录密码
//重置密码
mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)
mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.01 sec)
//修改密码
mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY '123456';
Query OK, 0 rows affected (0.00 sec)
mysql> quit //退出
Bye
//为避免mysql自动升级，这里需要卸载最开始安装的yum源
[root@Gin ~]# rpm -e mysql57-community-release3. mysql的程序组成
- 客户端
-
- mysql：CLI交互式客户端程序
- mysql_secure_installation：安全初始化，强烈建议安装完以后执行此命令
- mysqldump：mysql备份工具
- mysqladmin
- 服务器端
-
- mysqld
3.1 mysql工具使用
//语法：mysql [OPTIONS] [database]
//常用的OPTIONS：
-uUSERNAME //指定用户名，默认为root
-hHOST //指定服务器主机，默认为localhost，推荐使用ip地址
-pPASSWORD //指定用户的密码
-P# //指定数据库监听的端口，这里的#需用实际的端口号代替，如-P3307
-V //查看当前使用的mysql版本
-e //不登录mysql执行sql语句后退出，常用于脚本
[root@Gin ~]# mysql -V //查看当前的MySQL版本
mysql Ver 14.14 Distrib 5.7.38, for Linux (x86_64) using EditLine wrapper
//使用root的身份用IP登录127.0.0.1MySQL
[root@Gin ~]# mysql -uroot -p123456 -h127.0.0.1
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 5
Server version: 5.7.38 MySQL Community Server (GPL)
Copyright (c) 2000, 2022, Oracle and/or its affiliates.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
//注意，不推荐直接在命令行里直接用-pPASSWORD的方式登录，而是使用-p选项，然后交互式输入密码
[root@Gin ~]# mysql -uroot -p -h127.0.0.1
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 6
Server version: 5.7.38 MySQL Community Server (GPL)
Copyright (c) 2000, 2022, Oracle and/or its affiliates.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
//查看MySQL的库 注意这里只是进入后便退出了只将查询到的库打印出来
[root@Gin ~]# mysql -uroot -p -h127.0.0.1 -e 'show databases;'
Enter password:
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
3.2 服务器监听的两种socket地址
| socket类型 | 说明 |
| ip socket | 默认监听在tcp的3306端口，支持远程通信 |
| unix sock | 监听在sock文件上（/tmp/mysql.sock，/var/lib/mysql/mysql.sock） |
4. mysql数据库操作
4.1 DDL操作
4.1.1 数据库操作
//创建数据库
//语法：CREATE DATABASE [IF NOT EXISTS] 'DB_NAME';
//创建数据库Gin_A
mysql> create database if not exists Gin_A;
Query OK, 1 row affected (0.00 sec)
//查看当前实例有哪些数据库
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| Gin_A |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
//删除数据库
//语法：DROP DATABASE [IF EXISTS] 'DB_NAME';
//删除数据库wangqingge
mysql> drop database if exists Gin_A;
Query OK, 0 rows affected (0.00 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
4 rows in set (0.00 sec)
4.1.2 表操作
//创建表
//语法：CREATE TABLE table_name (col1 datatype 修饰符,col2 datatype 修饰符) ENGINE='存储引擎类型';
//在数据库wangqingge里创建表wangqing
mysql> create database Gin_A; //创建数据库Gin_A
Query OK, 1 row affected (0.00 sec)
mysql> use Gin_A; //进入Gin_A数据库
Database changed
mysql> create table Gin_A(id int not null,name varchar(100) not null,age tinyint);
Query OK, 0 rows affected (0.02 sec)
//查看当前数据库有哪些表
mysql> show tables;
+-----------------+
| Tables_in_Gin_A |
+-----------------+
| Gin_A |
+-----------------+
1 row in set (0.00 sec)
//删除表
//语法：DROP TABLE [ IF EXISTS ] 'table_name';
//删除表wangqing
mysql> drop table Gin_A;
Query OK, 0 rows affected (0.01 sec)
//查看数据库中的表
mysql> show tables;
Empty set (0.00 sec)4.1.3 用户操作
mysql用户帐号由两部分组成，如'USERNAME'@'HOST'，表示此USERNAME只能从此HOST上远程登录
这里（'USERNAME'@'HOST'）的HOST用于限制此用户可通过哪些主机远程连接mysql程序，其值可为：
- IP地址，如：172.16.12.129
- 通配符
-
- %：匹配任意长度的任意字符，常用于设置允许从任何主机登录
- _：匹配任意单个字符
//数据库用户创建
//语法：CREATE USER 'username'@'host' [IDENTIFIED BY 'password'];
//创建数据库用户wangqing
mysql> create user 'Gin'@'127.0.0.1' identified by 'Gin123';
Query OK, 0 rows affected (0.00 sec)
mysql> exit
Bye
//使用新创建的用户和密码登录
[root@Gin ~]# mysql -uGin -p -h127.0.0.1
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 10
Server version: 5.7.38 MySQL Community Server (GPL)
Copyright (c) 2000, 2022, Oracle and/or its affiliates.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
//删除数据库用户
//语法：DROP USER 'username'@'host';
mysql> drop user 'Gin'@'127.0.0.1'; //在删除用户时需要登录root用户来执行
Query OK, 0 rows affected (0.00 sec)4.1.4 查看命令SHOW
//查看所有字符集
mysql> show character set;
+----------+---------------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+---------------------------------+---------------------+--------+
| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |
| dec8 | DEC West European | dec8_swedish_ci | 1 |
| cp850 | DOS West European | cp850_general_ci | 1 |
| hp8 | HP West European | hp8_english_ci | 1 |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 |
| latin1 | cp1252 West European | latin1_swedish_ci | 1 |
| latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 |
| swe7 | 7bit Swedish | swe7_swedish_ci | 1 |
| ascii | US ASCII | ascii_general_ci | 1 |
...
...
//查看当前数据库支持的所有存储引擎
mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine | Support | Comment | Transactions | XA | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
| MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO |
| MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO |
| BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO |
| MyISAM | YES | MyISAM storage engine | NO | NO | NO |
| CSV | YES | CSV storage engine | NO | NO | NO |
| ARCHIVE | YES | Archive storage engine | NO | NO | NO |
| PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO |
| FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)
//查看数据库信息
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| Gin_A |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
//不进入某数据库而列出其包含的所有表
mysql> show tables from sys;
+-----------------------------------------------+
| Tables_in_sys |
+-----------------------------------------------+
| host_summary |
| host_summary_by_file_io |
...
...
//查看表结构
//语法：DESC [db_name.]table_name;
mysql> desc sys.host_summary;
+------------------------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------------------+---------------+------+-----+---------+-------+
| host | varchar(60) | YES | | NULL | |
| statements | decimal(64,0) | YES | | NULL | |
| statement_latency | text | YES | | NULL | |
| statement_avg_latency | text | YES | | NULL | |
| table_scans | decimal(65,0) | YES | | NULL | |
| file_ios | decimal(64,0) | YES | | NULL | |
| file_io_latency | text | YES | | NULL | |
| current_connections | decimal(41,0) | YES | | NULL | |
| total_connections | decimal(41,0) | YES | | NULL | |
| unique_users | bigint(21) | NO | | 0 | |
| current_memory | text | YES | | NULL | |
| total_memory_allocated | text | YES | | NULL | |
+------------------------+---------------+------+-----+---------+-------+
12 rows in set (0.00 sec)
//查看某表的创建命令
//语法：SHOW CREATE TABLE table_name;
mysql> show create table Gin_A.Gin_A;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
| Gin_A | CREATE TABLE `Gin_A` (
`id` int(11) NOT NULL,
`name` varchar(100) NOT NULL,
`age` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
//查看某表的状态
//语法：SHOW TABLE STATUS LIKE 'table_name'\G
mysql> use Gin_A; //进入数据库Gin_A
Database changed
mysql> show table status like 'Gin_A'\G //查看Gin_A表的状态
*************************** 1. row ***************************
Name: Gin_A
Engine: InnoDB
Version: 10
Row_format: Dynamic
Rows: 0
Avg_row_length: 0
Data_length: 16384
Max_data_length: 0
Index_length: 0
Data_free: 0
Auto_increment: NULL
Create_time: 2022-07-25 17:18:47
Update_time: NULL
Check_time: NULL
Collation: latin1_swedish_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
4.1.5 获取帮助
//获取命令使用帮助
//语法：HELP keyword;
mysql> HELP CREATE TABLE; //获取创建表的帮助
Name: 'CREATE TABLE'
Description:
Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
(create_definition,...)
[table_options]
[partition_options]
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
[(create_definition,...)]
[table_options]
[partition_options]
[IGNORE | REPLACE]
[AS] query_expression
......
......4.2 DML操作
DML操作包括增(INSERT)、删(DELETE)、改(UPDATE)、查(SELECT)，均属针对表的操作。
4.2.1 INSERT语句
//DML操作之增操作insert
//语法：INSERT [INTO] table_name [(column_name,...)] {VALUES | VALUE} (value1,...),(...),...
mysql> use Gin_A;
Database changed
//插入一条
mysql> insert into Gin_A(id,name,age) value(1,'tom',20); /
Query OK, 1 row affected (0.01 sec)
//插入多条
mysql> insert into Gin_A(id,name,age) values(2,'jerry',23),(3,'Gin',20),(4,'Kin',26);
Query OK, 3 rows affected (0.01 sec)
Records: 3 Duplicates: 0 Warnings: 0
注意：在最新版中values可以插入多条也可以插入一条4.2.2 SELECT语句
字段column表示法
| 表示符 | 代表什么？ |
| * | 所有字段 |
| as | 字段别名，如col1 AS alias1 |
条件判断语句WHERE
| 操作类型 | 常用操作符 |
| 操作符 | >，<，>=，<=，=，!= |
| 条件逻辑操作 | AND |
ORDER BY：排序，默认为升序（ASC）
| ORDER BY语句 | 意义 |
| ORDER BY ‘column_name' | 根据column_name进行升序排序 |
| ORDER BY 'column_name' DESC | 根据column_name进行降序排序 |
| ORDER BY ’column_name' LIMIT 2 | 根据column_name进行升序排序 |
| ORDER BY ‘column_name' LIMIT 1,2 | 根据column_name进行升序排序 |
//DML操作之查操作select
//语法：SELECT column1,column2,... FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];
mysql> use Gin_A;
Database changed
//查看内容
mysql> select * from Gin_A;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | Gin | 20 |
| 4 | Kin | 26 |
+----+-------+------+
4 rows in set (0.00 sec)
//查看字段
mysql> select name from Gin_A;
+-------+
| name |
+-------+
| tom |
| jerry |
| Gin |
| Kin |
+-------+
4 rows in set (0.00 sec)
//按照字段升序
mysql> select * from Gin_A order by age;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 1 | tom | 20 |
| 3 | Gin | 20 |
| 2 | jerry | 23 |
| 4 | Kin | 26 |
+----+-------+------+
4 rows in set (0.00 sec)
//按照字段降序
mysql> select * from Gin_A order by age desc;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 4 | Kin | 26 |
| 2 | jerry | 23 |
| 1 | tom | 20 |
| 3 | Gin | 20 |
+----+-------+------+
4 rows in set (0.00 sec)
//查找升序的前两位
mysql> select * from Gin_A order by age limit 2;
+----+------+------+
| id | name | age |
+----+------+------+
| 1 | tom | 20 |
| 3 | Gin | 20 |
+----+------+------+
2 rows in set (0.00 sec)
//查找升序不显示第一位显示后两位
mysql> select * from Gin_A order by age limit 1,2;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 3 | Gin | 20 |
| 2 | jerry | 23 |
+----+-------+------+
2 rows in set (0.00 sec)
//查找年龄大于或者等于23的数据
mysql> select * from Gin_A where age >= 23;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 2 | jerry | 23 |
| 4 | Kin | 26 |
+----+-------+------+
2 rows in set (0.00 sec)
//查找年龄大于或者等于23且名称位Kin的数据
mysql> select * from Gin_A where age >= 23 and name = 'Kin';
+----+------+------+
| id | name | age |
+----+------+------+
| 4 | Kin | 26 |
+----+------+------+
1 row in set (0.00 sec)
//查找年龄在23到26之间的数据
mysql> select * from Gin_A where age between 23 and 26;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 2 | jerry | 23 |
| 4 | Kin | 26 |
+----+-------+------+
2 rows in set (0.00 sec)
//查找年龄不为空的数据
mysql> select * from Gin_A where age is not null;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | Gin | 20 |
| 4 | Kin | 26 |
+----+-------+------+
4 rows in set (0.00 sec)
//查找年龄字段是空的数据
mysql> select * from wangqing where age is null;
+----+------+------+
| id | name | age |
+----+------+------+
| 7 | lisi | NULL |
+----+------+------+
1 row in set (0.00 sec)4.2.3 update语句
//DML操作之改操作update
//语法：UPDATE table_name SET column1 = new_value1[,column2 = new_value2,...] [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];
mysql> select * from Gin_A;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | Gin | 20 |
| 4 | Kin | 26 |
+----+-------+------+
4 rows in set (0.00 sec)
//修改表中的tom数据
mysql> update Gin_A set age = 30 where name = 'tom';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from Gin_A;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 1 | tom | 30 |
| 2 | jerry | 23 |
| 3 | Gin | 20 |
| 4 | Kin | 26 |
+----+-------+------+
4 rows in set (0.00 sec)
4.2.4 delete语句
//DML操作之删操作delete
//语法：DELETE FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];
mysql> select * from Gin_A;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 1 | tom | 30 |
| 2 | jerry | 23 |
| 3 | Gin | 20 |
| 4 | Kin | 26 |
+----+-------+------+
4 rows in set (0.00 sec)
//删除表的数据
mysql> delete from Gin_A where id = 4;
Query OK, 1 row affected (0.00 sec)
mysql> select * from Gin_A;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 1 | tom | 30 |
| 2 | jerry | 23 |
| 3 | Gin | 20 |
+----+-------+------+
3 rows in set (0.00 sec)
//删除整张表的内容
mysql> delete from Gin_A;
Query OK, 3 rows affected (0.01 sec)
mysql> select * from Gin_A;
Empty set (0.00 sec)
mysql> desc Gin_A;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(100) | NO | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)4.2.5 truncate语句
truncate与delete的区别：
| 语句类型 | 特点 |
| delete | DELETE删除表内容时仅删除内容，但会保留表结构 |
| truncate | 删除表中所有数据，且无法恢复 |
//语法：TRUNCATE table_name;
mysql> select * from Gin_A;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 1 | tom | 20 |
| 2 | jeery | 20 |
| 3 | kin | 23 |
| 4 | pin | 24 |
| 5 | gin | 25 |
| 6 | zz | 26 |
| 7 | li | NULL |
+----+-------+------+
7 rows in set (0.00 sec)
mysql> truncate Gin_A;
Query OK, 0 rows affected (0.02 sec)
mysql> select * from Gin_A;
Empty set (0.00 sec)
mysql> desc Gin_A;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(100) | NO | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)4.3 DCL操作
4.3.1 创建授权grant
权限类型(priv_type)
| 权限类型 | 代表什么？ |
| ALL | 所有权限 |
| SELECT | 读取内容的权限 |
| INSERT | 插入内容的权限 |
| UPDATE | 更新内容的权限 |
| DELETE | 删除内容的权限 |
指定要操作的对象db_name.table_name
| 表示方式 | 意义 |
| *.* | 所有库的所有表 |
| db_name | 指定库的所有表 |
| db_name.table_name | 指定库的指定表 |
WITH GRANT OPTION：被授权的用户可将自己的权限副本转赠给其他用户，说白点就是将自己的权限完全复制给另一个用户。不建议使用。
GRANT priv_type,... ON [object_type] db_name.table_name TO ‘username'@'host' [IDENTIFIED BY 'password'] [WITH GRANT OPTION];
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| Gin_A |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
//授权kin用户在数据库本机上登录访问所有数据库
mysql> grant all on *.* to 'kin'@'localhost' identified by '132456';
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> grant all on *.* to 'kin'@'127.0.0.1' identified by '132456';
Query OK, 0 rows affected, 1 warning (0.01 sec)
//授权kin用户在172.16.12.129上远程登录访问Gin_A数据库
mysql> grant all on Gin_A.* to 'kin'@'192.168.22.109' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)
//授权kin用户在所有位置上远程登录访问Gin_A数据库
mysql> grant all on *.* to 'kin'@'%' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)4.3.2 查看授权
//查看当前登录用户的授权信息
mysql> show grants;
+---------------------------------------------------------------------+
| Grants for root@localhost |
+---------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION |
+---------------------------------------------------------------------+
2 rows in set (0.00 sec)
//查看指定用户wangqing的授权信息
mysql> show grants for kin;
+------------------------------------------+
| Grants for kin@% |
+------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'kin'@'%' |
+------------------------------------------+
1 row in set (0.00 sec)
mysql> show grants for 'kin'@'localhost';
+--------------------------------------------------+
| Grants for kin@localhost |
+--------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'kin'@'localhost' |
+--------------------------------------------------+
1 row in set (0.00 sec)
mysql> show grants for 'kin'@'127.0.0.1';
+--------------------------------------------------+
| Grants for kin@127.0.0.1 |
+--------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'kin'@'127.0.0.1' |
+--------------------------------------------------+
1 row in set (0.00 sec)
mysql> show grants for 'kin'@'192.168.22.109';
+-------------------------------------------------------------+
| Grants for kin@192.168.22.109 |
+-------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'kin'@'192.168.22.109' |
| GRANT ALL PRIVILEGES ON `Gin_A`.* TO 'kin'@'192.168.22.109' |
+-------------------------------------------------------------+
2 rows in set (0.00 sec)4.3.3 使用远程连接工具登录
4.3.4 取消授权REVOKE
//语法：REVOKE priv_type,... ON db_name.table_name FROM 'username'@'host';
mysql> revoke all on *.* from 'kin'@'192.168.22.109';
Query OK, 0 rows affected (0.00 sec)
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)注意：mysql服务进程启动时会读取mysql库中的所有授权表至内存中：
- GRANT或REVOKE等执行权限操作会保存于表中，mysql的服务进程会自动重读授权表，并更新至内存中
- 对于不能够或不能及时重读授权表的命令，可手动让mysql的服务进程重读授权表
mysql> FLUSH PRIVILEGES;实战案例
1.搭建mysql服务
//配置mysql的yum源
[root@Gin ~]# wget http://dev.mysql.com/get/mysql57-community-release-el7-11.noarch.rpm
[root@Gin ~]# rpm -Uvh mysql57-community-release-el7-11.noarch.rpm
[root@Gin ~]# yum module disable mysql
//安装mysql5.7版本的因为开源免费
[root@Gin ~]# dnf -y install mysql-community-server mysql-community-client mysql-community-common mysql-community-devel --nogpgcheck
#启动mysql并设置开机自动启动
[root@Gin src]# systemctl enable --now mysqld
#启动mysql并设置开机自动启动
[root@Gin ~]# ss -anltup | grep mysql
tcp LISTEN 0 80 *:3306 *:* users:(("mysqld",pid=1778,fd=29))
#使用获取到的临时密码登录mysql
[root@Gin src]# grep "password" /var/log/mysqld.log
2022-07-25T02:05:53.996584Z 1 [Note] A temporary password is generated for root@localhost: As5sjtwGgF=L #临时密码
2022-07-25T02:05:33.375577Z 2 [Note] Access denied for user 'root'@'localhost' (using password: YES)
[root@Gin src]#
#使用获取到的临时密码登录mysql
[root@Gin src]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.38
Copyright (c) 2000, 2022, Oracle and/or its affiliates.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> //看到有这样的标识符则表示成功登录了
//修改mysql登录密码
mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)
#设置全局validate\u password\u策略=0；
mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.00 sec)
#设置全局validate\u password\u length=1；
mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'long123!';
Query OK, 0 rows affected (0.00 sec)
mysql>
//为避免mysql自动升级，这里需要卸载最开始安装的yum源
[root@Gin src]# rpm -e mysql57-community-release 2.创建一个以你名字为名的数据库，并创建一张表student，该表包含三个字段（id，name，age），表结构如下：
mysql> desc student;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(100) | NO | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+--------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)#创建数据库
mysql> create database lf;
Query OK, 1 row affected (0.00 sec)
//查看当前实例有哪些数据库
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| lf |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
mysql>
mysql> show tables;
+--------------------+
| Tables_in_lf |
+--------------------+
| lingbo |
+--------------------+
1 row in set (0.00 sec)
mysql> create table student(id int(11) primary key auto_increment,name varchar(100) not null,age tinyint(4));
Query OK, 0 rows affected (0.00 sec)
mysql> desc student;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(100) | NO | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+--------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
mysql> 3.查看下该新建的表有无内容（用select语句）
#select语句查看
mysql> select * from student;
Empty set (0.00 sec)
mysql> 4.往新建的student表中插入数据（用insert语句），结果应如下所示：
+----+-------------+------+
| id | name | age |
+----+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 6 | zhangshan | 20 |
| 7 | lisi | NULL |
| 8 | chenshuo | 10 |
| 9 | wangwu | 3 |
| 10 | qiuyi | 15 |
| 11 | qiuxiaotian | 20 |
+----+-------------+------+
mysql> insert into student (name,age) values('tom',20),('jerry',23),('wangqing',25),('sean',28),('zhangshan',26),('zhangsan',20),('lisi',null),('chenshuo',10),('wangwu',3),('qiuyi',15),('qiuxiaotian',20);
Query OK, 11 rows affected (0.01 sec)
Records: 11 Duplicates: 0 Warnings: 0
#插入成功
mysql> select * from student;
+----+-------------+------+
| id | name | age |
+----+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 6 | zhangsan | 20 |
| 7 | lisi | NULL |
| 8 | chenshuo | 10 |
| 9 | wangwu | 3 |
| 10 | qiuyi | 15 |
| 11 | qiuxiaotian | 20 |
+----+-------------+------+
11 rows in set (0.00 sec)
mysql>
5.修改lisi的年龄为50
mysql> update student set age = 50 where name = 'lisi';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from student where name = 'lisi';
+----+------+------+
| id | name | age |
+----+------+------+
| 7 | lisi | 50 |
+----+------+------+
1 row in set (0.00 sec)
mysql> 6.以age字段降序排序
mysql> select * from student order by age desc;
+----+-------------+------+
| id | name | age |
+----+-------------+------+
| 7 | lisi | 50 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 3 | wangqing | 25 |
| 2 | jerry | 23 |
| 1 | tom | 20 |
| 6 | zhangsan | 20 |
| 11 | qiuxiaotian | 20 |
| 10 | qiuyi | 15 |
| 8 | chenshuo | 10 |
| 9 | wangwu | 3 |
+----+-------------+------+
11 rows in set (0.00 sec)
mysql>
7.查询student表中年龄最小的3位同学跳过前2位
mysql> select * from student order by age limit 2,3;
+----+-------------+------+
| id | name | age |
+----+-------------+------+
| 10 | qiuyi | 15 |
| 1 | tom | 20 |
| 11 | qiuxiaotian | 20 |
+----+-------------+------+
3 rows in set (0.00 sec)
mysql>
8.查询student表中年龄最大的4位同学
mysql> select * from student order by age desc limit 4;
+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 7 | lisi | 50 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 3 | wangqing | 25 |
+----+-----------+------+
4 rows in set (0.01 sec)
mysql>
9.查询student表中名字叫zhangshan的记录
mysql> select * from student where name = 'zhangshan';
+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 5 | zhangshan | 26 |
+----+-----------+------+
1 row in set (0.00 sec)
mysql> 10.查询student表中名字叫zhangshan且年龄大于20岁的记录
mysql> select * from student where name = 'zhangshan' and age > 20;
+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 5 | zhangshan | 26 |
+----+-----------+------+
1 row in set (0.01 sec)
mysql> 11.查询student表中年龄在23到30之间的记录
#第一种查询方法
mysql> select * from student where age between 23 and 30;
+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
+----+-----------+------+
4 rows in set (0.00 sec)
#第二种查询方法
mysql> select * from student where age >=23 and age <= 30;
+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
+----+-----------+------+
4 rows in set (0.00 sec)
mysql> 12.修改wangwu的年龄为100
mysql> update student set age = 100 where name = 'wangwu';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from student where name = 'wangwu';
+----+--------+------+
| id | name | age |
+----+--------+------+
| 9 | wangwu | 100 |
+----+--------+------+
1 row in set (0.00 sec)
mysql> 13.删除student中名字叫zhangshan且年龄小于等于20的记录
mysql> delete from student where name = 'zhangshan' and age >= 20;
Query OK, 1 row affected (0.00 sec)
#查看表观察是否删除成功
mysql> select * from student;
+----+-------------+------+
| id | name | age |
+----+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 6 | zhangsan | 20 |
| 7 | lisi | 50 |
| 8 | chenshuo | 10 |
| 9 | wangwu | 100 |
| 10 | qiuyi | 15 |
| 11 | qiuxiaotian | 20 |
+----+-------------+------+
10 rows in set (0.00 sec)
mysql> 
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