Linux服务管理-mysql基础

mysql基础

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

SQL：Structure Query Language，结构化查询语言

SQL 约束：constraint，用于限制加入表的数据的类型。

• NOT NULL - 指示某列不能存储 NULL 值。
• UNIQUE - 保证某列的每行必须有唯一的值。
• PRIMARY KEY - NOT NULL 和 UNIQUE 的结合。确保某列（或两个列多个列的结合）有唯一标识，有助于更容易更快速地找到表中的一个特定的记录。
• FOREIGN KEY - 保证一个表中的数据匹配另一个表中的值的参照完整性。
• CHECK - 保证列中的值符合指定的条件。
• DEFAULT - 规定没有给列赋值时的默认值。

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 DROP：删除 ALTER：修改
DML	INSERT：向表中插入数据 DELETE：删除表中数据 UPDATE：更新表中数据 SELECT：查询表中数据
DCL	GRANT：授权 REVOKE：移除授权

2. mysql安装与配置

由于MySQL和MariaDB是同一个开发团队制作的软件，所以操作方式差不多，而且MariaDB是免费的，这里就用MariaDB作为演示。

2.1 mariadb安装

[root@localhost ~]# yum -y install mariadb*

2.2 mariadb配置

//设置mariadb开机自动启动
[root@localhost ~]# systemctl enable --now mariadb

//确保3306端口已经监听起来
[root@localhost ~]# ss -antl
State       Recv-Q Send-Q Local Address:Port               Peer Address:Port              
LISTEN      0      100    127.0.0.1:25                        *:*                  
LISTEN      0      50            *:3306                      *:*                  
LISTEN      0      128           *:22                        *:*                  
LISTEN      0      100       [::1]:25                     [::]:*                  
LISTEN      0      128        [::]:22                     [::]:*     

//登录mariadb
[root@localhost ~]# mysql   
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.65-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]>         //看到有这样的标识符则表示成功登录了

//设置mariadb登录密码
MariaDB [(none)]> set password = password('12321');
Query OK, 0 rows affected (0.00 sec)

//修改密码后登录
[root@localhost ~]# mysql -uroot -p12321
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 3
Server version: 5.5.65-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> 

3. 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
    
//查看版本信息    
[root@localhost ~]# mysql -V
mysql  Ver 15.1 Distrib 5.5.65-MariaDB, for Linux (x86_64) using readline 5.1

//指定服务器主机（必须先授权才能连接）
//如：客户机IP：192.168.118.133  服务器IP：192.168.118.134
//服务器操作：
[root@localhost ~]# mysql -uroot -p12321
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 4
Server version: 5.5.65-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> grant all on *.* to 'root'@192.168.118.133 identified by '12321';Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> flush privileges;
Query OK, 0 rows affected (0.00 sec)
//现在客户机可以连接服务器了：
[root@localhost ~]# mysql -uroot -p12321 -h192.168.118.134
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 5
Server version: 5.5.65-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> 

//使用交互式输入密码
[root@localhost ~]# mysql -u root -p
Enter password:    //输入密码
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 8
Server version: 5.5.65-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> 

//不登录mysql执行sql语句
[root@localhost ~]# mysql -uroot -p12321 -e'show databases;'
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| test               |
+--------------------+

3.2 服务器监听的两种socket地址

• 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）
    仅支持本地通信

  //通过sock文件连接
  [root@localhost ~]# mysql -uroot -p12321 -S /var/lib/mysql/mysql.sock 
  Welcome to the MariaDB monitor.  Commands end with ; or \g.
  Your MariaDB connection id is 14
  Server version: 5.5.65-MariaDB MariaDB Server
  
  Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
  
  Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
  
  MariaDB [(none)]> 
  

  • server地址只能是：localhost，127.0.0.1

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school
MariaDB [(none)]> create database if not exists school;
Query OK, 1 row affected (0.00 sec)

//查看当前实例有哪些数据库
MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| school             |
| test               |
+--------------------+
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school
MariaDB [(none)]> drop database if exists school;
Query OK, 0 rows affected, 1 warning (0.00 sec)

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| test               |
+--------------------+
4 rows in set (0.01 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school里创建表20200520
MariaDB [(none)]> create database school;     //创建数据库school
Query OK, 1 row affected (0.00 sec)

MariaDB [(none)]> use school;            //进入school数据库
Database changed
MariaDB [school]> create table Linux0520(id int not null,name varchar(50) not null,age tinyint not null);
Query OK, 0 rows affected (0.01 sec)

//查看当前数据库有哪些表
MariaDB [school]> show tables;
+------------------+
| Tables_in_school |
+------------------+
| Linux0520        |
+------------------+
1 row in set (0.00 sec)

//删除表
//语法：DROP TABLE [ IF EXISTS ] 'table_name';
//删除表school
MariaDB [school]> drop table Linux0520;
Query OK, 0 rows affected (0.00 sec)

MariaDB [school]> 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tom
MariaDB [(none)]> create user 'tom'@'127.0.0.1' identified by '12321';
Query OK, 0 rows affected (0.05 sec)

//使用新创建的用户和密码登录
[root@localhost ~]# mysql -utom -p12321 -h127.0.0.1 
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 3
Server version: 5.5.65-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> 

//删除数据库用户
//语法：DROP USER 'username'@'host'; 
MariaDB [(none)]> drop user 'tom'@'127.0.0.1';
Query OK, 0 rows affected (0.01 sec)

4.1.4 查看命令SHOW

• 查看支持的所有字符集

MariaDB [(none)]> 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 |
......
......

• 查看当前数据库支持的所有存储引擎

//第一种方法
MariaDB [(none)]> show engines;        
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                                          | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
| InnoDB             | DEFAULT | Percona-XtraDB, Supports transactions, row-level locking, and foreign keys       | YES          | YES  | YES        |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                                            | NO           | NO   | NO         |
| MyISAM             | YES     | Non-transactional engine with good performance and small data footprint          | NO           | NO   | NO         |
......
......

//第二种方法
MariaDB [(none)]> show engines\G
*************************** 1. row ***************************
      Engine: InnoDB
     Support: DEFAULT
     Comment: Percona-XtraDB, Supports transactions, row-level locking, and foreign keys
Transactions: YES
          XA: YES
  Savepoints: YES
*************************** 2. row ***************************
      Engine: MRG_MYISAM
     Support: YES
     Comment: Collection of identical MyISAM tables
Transactions: NO
          XA: NO
  Savepoints: NO
......
......

• 查看数据库信息

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| school             |
| test               |
+--------------------+
5 rows in set (0.07 sec)

• 不进入某数据库而列出其包含的所有表

MariaDB [(none)]> show tables from school;
+------------------+
| Tables_in_school |
+------------------+
| Linux0520        |
+------------------+
1 row in set (0.00 sec)

• 查看某表的创建命令

MariaDB [(none)]> show create table school.Linux0520;
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table     | Create Table                                                                                                                                          |
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------+
| Linux0520 | CREATE TABLE `Linux0520` (
  `id` int(11) NOT NULL,
  `name` varchar(50) NOT NULL,
  `age` tinyint(4) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-----------+-------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

• 查看某表的状态

MariaDB [school]> use school;         //进入数据库school
Database changed
MariaDB [school]> show table status like 'Linux0520'\G
*************************** 1. row ***************************
           Name: Linux0520
         Engine: InnoDB
        Version: 10
     Row_format: Compact
           Rows: 0
 Avg_row_length: 0
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 10485760
 Auto_increment: NULL
    Create_time: 2020-05-21 02:17:42
    Update_time: NULL
     Check_time: NULL
      Collation: latin1_swedish_ci
       Checksum: NULL
 Create_options: 
        Comment: 
1 row in set (0.00 sec)

• 查看表结构

MariaDB [(none)]> desc school.Linux0520;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   |     | NULL    |       |
| name  | varchar(50) | NO   |     | NULL    |       |
| age   | tinyint(4)  | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.01 sec)

4.1.5 获取帮助

//获取命令使用帮助
//语法：HELP keyword;
MariaDB [(none)]> 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]

Or:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    [(create_definition,...)]
    [table_options]
    [partition_options]
    select_statement
......
......

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,...),(...),...

• 一次插入一条记录

MariaDB [(none)]> use school;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
MariaDB [school]> insert into Linux0520 (id,name,age) value (1,'tom',20);
Query OK, 1 row affected (0.00 sec)

• 一次插入多条记录

MariaDB [school]> insert into Linux0520 (id,name,age) values (2,'jerry',23),(3,'jack',18),(4,'zhangsan',25),(5,'lisi',26),(6,'wangwu',NULL);
Query OK, 5 rows affected, 1 warning (0.00 sec)
Records: 5  Duplicates: 0  Warnings: 1

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 当表名很长时用别名代替

条件判断语句WHERE

操作类型	常用操作符
操作符	>，<，>=，<=，=，!= BETWEEN column# AND column# LIKE：模糊匹配 RLIKE：基于正则表达式进行模式匹配 IS NOT NULL：非空 IS NULL：空
条件逻辑操作	AND OR NOT

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 并只取前2个结果
ORDER BY ‘column_name’ LIMIT 1,2	根据column_name进行升序排序 并且略过第1个结果取后面的2个结果

//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];

• 查询表内所有内容

MariaDB [school]> select * from Linux0520
    -> ;
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  1 | tom      |  20 |
|  2 | jerry    |  23 |
|  3 | jack     |  18 |
|  4 | zhangsan |  25 |
|  5 | lisi     |  26 |
|  6 | wangwu   |   0 |
+----+----------+-----+
6 rows in set (0.00 sec)

• 将id临时别名为学生编号

MariaDB [school]> select id as 学生编号,name from Linux0520;
+--------------+----------+
| 学生编号     | name     |
+--------------+----------+
|            1 | tom      |
|            2 | jerry    |
|            3 | jack     |
|            4 | zhangsan |
|            5 | lisi     |
|            6 | wangwu   |
+--------------+----------+
6 rows in set (0.00 sec)

• 按年龄大小排序

MariaDB [school]> select * from Linux0520 where age is not null order by age;
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  6 | wangwu   |   0 |
|  3 | jack     |  18 |
|  1 | tom      |  20 |
|  2 | jerry    |  23 |
|  4 | zhangsan |  25 |
|  5 | lisi     |  26 |
+----+----------+-----+
6 rows in set (0.00 sec)

• 按年龄大小倒序排序

MariaDB [school]> select * from Linux0520 order by age desc;
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  5 | lisi     |  26 |
|  4 | zhangsan |  25 |
|  2 | jerry    |  23 |
|  1 | tom      |  20 |
|  3 | jack     |  18 |
|  6 | wangwu   |   0 |
+----+----------+-----+
6 rows in set (0.00 sec)

• 按年龄大小排序并只取前2个结果

MariaDB [school]> select * from Linux0520 order by age limit 2;
+----+--------+-----+
| id | name   | age |
+----+--------+-----+
|  6 | wangwu |   0 |
|  3 | jack   |  18 |
+----+--------+-----+
2 rows in set (0.00 sec)

• 按年龄排序并跳过1位取2位

MariaDB [school]> select * from Linux0520 order by age limit 1,2;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  3 | jack |  18 |
|  1 | tom  |  20 |
+----+------+-----+
2 rows in set (0.00 sec)

• 查询年龄最小的

MariaDB [school]> select * from Linux0520 order by age limit 1;
+----+--------+-----+
| id | name   | age |
+----+--------+-----+
|  6 | wangwu |   0 |
+----+--------+-----+
1 row in set (0.00 sec)

• 查询年龄最大的

MariaDB [school]> select * from Linux0520 order by age desc limit 1;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  5 | lisi |  26 |
+----+------+-----+
1 row in set (0.00 sec)

• 查询年龄大于20岁的

MariaDB [school]> select * from Linux0520 where age > 20;
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  2 | jerry    |  23 |
|  4 | zhangsan |  25 |
|  5 | lisi     |  26 |
+----+----------+-----+
3 rows in set (0.01 sec)

• 查询年龄大于20岁并且名字叫zahngsan的

MariaDB [school]> select * from Linux0520 where age > 20 and name = 'zhangsan';
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  4 | zhangsan |  25 |
+----+----------+-----+
1 row in set (0.00 sec)

• 查询年龄在23到26的

MariaDB [school]> select * from Linux0520 where age between 23 and 26;
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  2 | jerry    |  23 |
|  4 | zhangsan |  25 |
|  5 | lisi     |  26 |
+----+----------+-----+
3 rows in set (0.00 sec)

• 查询年龄不是空的

MariaDB [school]> select * from Linux0520 where age is not null;
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  1 | tom      |  20 |
|  2 | jerry    |  23 |
|  3 | jack     |  18 |
|  4 | zhangsan |  25 |
|  5 | lisi     |  26 |
|  6 | wangwu   |   0 |
+----+----------+-----+
6 rows in set (0.00 sec)

• 查询年龄是23和名字是lisi的

MariaDB [school]> select * from Linux0520 where age = 23 or name = 'lisi';
+----+-------+-----+
| id | name  | age |
+----+-------+-----+
|  2 | jerry |  23 |
|  5 | lisi  |  26 |
+----+-------+-----+
2 rows in set (0.00 sec)

• 模糊匹配年龄是2开头的

MariaDB [school]> select * from Linux0520 where age like '2%';
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  1 | tom      |  20 |
|  2 | jerry    |  23 |
|  4 | zhangsan |  25 |
|  5 | lisi     |  26 |
+----+----------+-----+
4 rows in set (0.01 sec)

• 基于正则表达式进行模式匹配

MariaDB [school]> select * from Linux0520 where age rlike '1[0-9]';     //查询年龄是1开头的
+----+------+-----+
| id | name | age |
+----+------+-----+
|  3 | jack |  18 |
+----+------+-----+
1 row in set (0.00 sec)

MariaDB [school]> select * from Linux0520 where name rlike '^[a-z]{3}$';    //查名字是3个字母的
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  20 |
+----+------+-----+
1 row in set (0.00 sec)

GROUP BY：分组，用于结合聚合函数，根据一个或多个列对结果集进行分组

//语法：SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name;

//表websites的数据
MariaDB [RUNOOB]> use RUNOOB;
Database changed

MariaDB [RUNOOB]> select * from websites;
+----+--------------+---------------------------+-------+---------+
| id | name         | url                       | alexa | country |
+----+--------------+---------------------------+-------+---------+
|  1 | Google       | https://www.google.cm/    |     1 | USA     |
|  2 | 淘宝         | https://www.taobao.com/   |    13 | CN      |
|  3 | 菜鸟教程     | http://www.runoob.com/    |  4689 | CN      |
|  4 | 微博         | http://weibo.com/         |    20 | CN      |
|  5 | Facebook     | https://www.facebook.com/ |     3 | USA     |
+----+--------------+---------------------------+-------+---------+
5 rows in set (0.00 sec)

//表access_log的数据
MariaDB [RUNOOB]> select * from access_log;
+-----+---------+-------+------------+
| aid | site_id | count | date       |
+-----+---------+-------+------------+
|   1 |       1 |    45 | 2016-05-10 |
|   2 |       3 |   100 | 2016-05-13 |
|   3 |       1 |   230 | 2016-05-14 |
|   4 |       2 |    10 | 2016-05-14 |
|   5 |       5 |   205 | 2016-05-14 |
|   6 |       4 |    13 | 2016-05-15 |
|   7 |       3 |   220 | 2016-05-15 |
|   8 |       5 |   545 | 2016-05-16 |
|   9 |       3 |   201 | 2016-05-17 |
+-----+---------+-------+------------+
9 rows in set (0.00 sec)

• 统计 access_log 各个 site_id 的访问量

MariaDB [RUNOOB]> select site_id, sum(access_log.count) as num from access_log group by site_id;
+---------+------+
| site_id | num  |
+---------+------+
|       1 |  275 |
|       2 |   10 |
|       3 |  521 |
|       4 |   13 |
|       5 |  750 |
+---------+------+
5 rows in set (0.00 sec)

• 统计有记录的网站的记录数量（多表连接）

MariaDB [RUNOOB]> select websites.name,count(access_log.aid) as nums from access_log left join websites on access_log.site_id=websites.id group by websites.name;
+--------------+------+
| name         | nums |
+--------------+------+
| Facebook     |    2 |
| Google       |    2 |
| 微博         |    1 |
| 淘宝         |    1 |
| 菜鸟教程     |    3 |
+--------------+------+
5 rows 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];

MariaDB [school]> select * from Linux0520;
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  1 | tom      |  20 |
|  2 | jerry    |  23 |
|  3 | jack     |  18 |
|  4 | zhangsan |  25 |
|  5 | lisi     |  26 |
|  6 | wangwu   |   0 |
+----+----------+-----+
6 rows in set (0.00 sec)

MariaDB [school]> update Linux0520 set age = 30 where name = 'lisi';    //将lisi的年龄修改为30岁
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [school]> select * from Linux0520 where name = 'lisi';
+----+------+-----+
| id | name | age |
+----+------+-----+
|  5 | lisi |  30 |
+----+------+-----+
1 row 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];

MariaDB [school]> select * from Linux0520;
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  1 | tom      |  20 |
|  2 | jerry    |  23 |
|  3 | jack     |  18 |
|  4 | zhangsan |  25 |
|  5 | lisi     |  30 |
|  6 | wangwu   |   0 |
+----+----------+-----+
6 rows in set (0.00 sec)

• 删除某条记录

MariaDB [school]> delete from Linux0520 where id = 6;
Query OK, 1 row affected (0.00 sec)

MariaDB [school]> select * from Linux0520;
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  1 | tom      |  20 |
|  2 | jerry    |  23 |
|  3 | jack     |  18 |
|  4 | zhangsan |  25 |
|  5 | lisi     |  30 |
+----+----------+-----+
5 rows in set (0.00 sec)

• 删除整张表的内容

MariaDB [school]> delete from Linux0520;
Query OK, 5 rows affected (0.00 sec)

MariaDB [school]> select * from Linux0520;
Empty set (0.00 sec)

MariaDB [school]> desc Linux0520;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   |     | NULL    |       |
| name  | varchar(50) | NO   |     | NULL    |       |
| age   | tinyint(4)  | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.06 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 DELETE语句每次删除一行，并在事务日志中为所删除的每行记录一项 可以通过回滚事务日志恢复数据 非常占用空间
truncate	删除表中所有数据，且无法恢复 表结构、约束和索引等保持不变，新添加的行计数值重置为初始值 执行速度比DELETE快，且使用的系统和事务日志资源少 通过释放存储表数据所用的数据页来删除数据，并且只在事务日志中记录页的释放 对于有外键约束引用的表，不能使用TRUNCATE TABLE删除数据 不能用于加入了索引视图的表

//语法：TRUNCATE table_name;
MariaDB [school]> select * from Linux0520; 
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  1 | tom      |  20 |
|  2 | jerry    |  23 |
|  3 | jack     |  18 |
|  4 | zhangsan |  25 |
|  5 | lisi     |  26 |
|  6 | wangwu   |   0 |
+----+----------+-----+
6 rows in set (0.00 sec)

MariaDB [school]> truncate Linux0520;
Query OK, 0 rows affected (0.00 sec)

MariaDB [school]> select * from Linux0520; 
Empty set (0.00 sec)

MariaDB [school]> desc Linux0520;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   |     | NULL    |       |
| name  | varchar(50) | NO   |     | NULL    |       |
| age   | tinyint(4)  | NO   |     | 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。

//语法：GRANT priv_type,... ON [object_type] db_name.table_name TO ‘username'@'host' [IDENTIFIED BY 'password'] [WITH GRANT OPTION];

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| school             |
| test               |
+--------------------+
5 rows in set (0.05 sec)

//授权tom用户在数据库本机上登录访问所有数据库
MariaDB [(none)]> grant all on *.* to 'tom'@'localhost' identified by '12321';
Query OK, 0 rows affected (0.01 sec)

MariaDB [(none)]> grant all on *.* to 'tom'@'127.0.0.1' identified by '12321';
Query OK, 0 rows affected (0.00 sec)

//授权tom用户在192.168.118.133上远程登录访问school数据库
MariaDB [(none)]> grant all on school.* to 'tom'@'192.168.118.133' identified by '12321';
Query OK, 0 rows affected (0.00 sec)

//授权tom用户在所有位置上远程登录访问school数据库
MariaDB [(none)]> grant all on *.* to 'tom'@'%' identified by '12321';
Query OK, 0 rows affected (0.00 sec)

//授权tom用户school数据库的Linux0520表的插入权限
MariaDB [school]> grant insert on school.Linux0520 to 'tom'@'localhost' identified by '12321';
Query OK, 0 rows affected (0.00 sec)

4.3.2 查看授权

• 查看当前登录用户的授权信息

MariaDB [school]> show grants;
+----------------------------------------------------------------------------------------------------------------------------------------+
| Grants for root@localhost                                                                                                              |
+----------------------------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' IDENTIFIED BY PASSWORD '*045C8A3B828B8D7674941C5D03E5961BAB546F9A' 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tom的授权信息

MariaDB [school]> show grants for tom;
+-------------------------------------------------------------------------------------------------------------+
| Grants for tom@%                                                                                            |
+-------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'tom'@'%' IDENTIFIED BY PASSWORD '*045C8A3B828B8D7674941C5D03E5961BAB546F9A' |
+-------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

MariaDB [school]> show grants for 'tom'@'localhost';
+---------------------------------------------------------------------------------------------------------------------+
| Grants for tom@localhost                                                                                            |
+---------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'tom'@'localhost' IDENTIFIED BY PASSWORD '*045C8A3B828B8D7674941C5D03E5961BAB546F9A' |
| GRANT INSERT ON `school`.`Linux0520` TO 'tom'@'localhost'                                                           |
+---------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

4.3.3 取消授权REVOKE

//语法：REVOKE priv_type,... ON db_name.table_name FROM 'username'@'host';

MariaDB [school]> revoke all on *.* from 'tom'@'localhost';
Query OK, 0 rows affected (0.00 sec)

MariaDB [school]> 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;

4.3.4 MySQL密码破解

//mysql -uroot -p 输入密码回车后，出现如下图错误。这时候需要我们破解密码。
[root@localhost ~]# mysql -uroot -p'hello'
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)

• 停止mysql服务

[root@localhost ~]# systemctl stop mariadb

• 编辑mysql配置文件

[root@localhost ~]# vim /etc/my.cnf
[mysqld]
skip-grant-tables    //添加该行代码开机跳过授权表
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
......
......

• 重启mysql数据库并进入数据库

[root@localhost ~]# systemctl restart mariadb
[root@localhost ~]# mysql -uroot -p
Enter password:     //直接回车
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.65-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]>     //成功进入数据库

• 选择mysql数据库并更改密码

MariaDB [(none)]> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
MariaDB [mysql]> update user set password=password('123456') where user="root";    //更改密码
Query OK, 4 rows affected (0.00 sec)
Rows matched: 4  Changed: 4  Warnings: 0

• 退出数据库并把刚在配置文件里添加的代码删除，然后重启服务

MariaDB [mysql]> quit
Bye
[root@localhost ~]# vim /etc/my.cnf      //删除skip-grant-tables
[root@localhost ~]# cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
......
......
[root@localhost ~]# systemctl restart mariadb

• 使用更改后的密码连接数据库

[root@localhost ~]# mysql -uroot -p'123456'
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.65-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]>     //成功连接说明密码破解成功

5. 实例

5.1 搭建mysql服务

[root@localhost ~]# yum -y install mariadb*
[root@localhost ~]# systemctl enable --now mariadb
Created symlink from /etc/systemd/system/multi-user.target.wants/mariadb.service to /usr/lib/systemd/system/mariadb.service.                
[root@localhost ~]# ss -antl | grep 3306    
LISTEN     0      50           *:3306                     *:* 
[root@localhost ~]# mysql
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.65-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> set password = password('123456');    //设置mysql密码
Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> quit
Bye
[root@localhost ~]# mysql -uroot -p123456    //用密码登录mysql
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 3
Server version: 5.5.65-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> 

5.2 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)

MariaDB [(none)]> create database linux;
Query OK, 1 row affected (0.00 sec)

MariaDB [(none)]> use linux;
Database changed
MariaDB [linux]> create table student(id int primary key auto_increment not null,name varchar(100) not null,age tinyint(4));
Query OK, 0 rows affected (0.01 sec)

MariaDB [linux]> 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)

5.3 查看下该新建的表有无内容（用select语句）

MariaDB [linux]> select * from student;
Empty set (0.00 sec)

5.4 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 |
+----+-------------+------+

MariaDB [linux]> insert into student(name,age) values('tom',20),('jerry',23),('wangqing',25),('sean',28),('zhangshan',26),('zhangshan',20);
Query OK, 6 rows affected (0.00 sec)
Records: 6  Duplicates: 0  Warnings: 0

MariaDB [linux]> insert into student(name) value('lisi');
Query OK, 1 row affected (0.00 sec)

MariaDB [linux]> insert into student(name,age) values('chenshuo',10),('wangwu',3),('qiuyi',15),('qiuxiaotian',20);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

MariaDB [linux]> select * from student;
+----+-------------+------+
| 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 |
+----+-------------+------+
11 rows in set (0.00 sec)

5.5 修改lisi的年龄为50

MariaDB [linux]> update student set age = 50 where name = 'lisi';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [linux]> select * from student where name = 'lisi';
+----+------+------+
| id | name | age  |
+----+------+------+
|  7 | lisi |   50 |
+----+------+------+
1 row in set (0.00 sec)

5.6 以age字段降序排序

MariaDB [linux]> 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 | zhangshan   |   20 |
| 11 | qiuxiaotian |   20 |
| 10 | qiuyi       |   15 |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |    3 |
+----+-------------+------+
11 rows in set (0.00 sec)

5.7 查询student表中年龄最小的3位同学跳过前2位

MariaDB [linux]> select * from student order by age limit 2,3;
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
| 10 | qiuyi     |   15 |
|  1 | tom       |   20 |
|  6 | zhangshan |   20 |
+----+-----------+------+
3 rows in set (0.00 sec)

5.8 查询student表中年龄最大的4位同学

MariaDB [linux]> 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 (0.00 sec)

5.9 查询student表中名字叫zhangshan的记录

MariaDB [linux]> select * from student where name = 'zhangshan';
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  5 | zhangshan |   26 |
|  6 | zhangshan |   20 |
+----+-----------+------+
2 rows in set (0.00 sec)

5.10 查询student表中名字叫zhangshan且年龄大于20岁的记录

MariaDB [linux]> select * from student where name = 'zhangshan' and age > 20; 
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  5 | zhangshan |   26 |
+----+-----------+------+
1 row in set (0.00 sec)

5.11 查询student表中年龄在23到30之间的记录

MariaDB [linux]> select * from student where age between 20 and 30;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  1 | tom         |   20 |
|  2 | jerry       |   23 |
|  3 | wangqing    |   25 |
|  4 | sean        |   28 |
|  5 | zhangshan   |   26 |
|  6 | zhangshan   |   20 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+
7 rows in set (0.00 sec)

5.12 修改wangwu的年龄为100

MariaDB [linux]> update student set age = 100 where name = 'wangwu';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [linux]> select * from student where name = 'wangwu'; 
+----+--------+------+
| id | name   | age  |
+----+--------+------+
|  9 | wangwu |  100 |
+----+--------+------+
1 row in set (0.00 sec)

5.13 删除student中名字叫zhangshan且年龄小于等于20的记录

MariaDB [linux]> delete from student where name = 'zhangshan' and age <= 20;
Query OK, 1 row affected (0.00 sec)

MariaDB [linux]> select * from student;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  1 | tom         |   20 |
|  2 | jerry       |   23 |
|  3 | wangqing    |   25 |
|  4 | sean        |   28 |
|  5 | zhangshan   |   26 |
|  7 | lisi        |   50 |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |  100 |
| 10 | qiuyi       |   15 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+
10 rows in set (0.00 sec)