MySQL 数据库学习（一）认识数据库

1 案例1：构建MySQL服务器

1.1 问题

1. 在IP地址192.168.88.50主机和192.168.88.51主机上部署mysql服务
2. 练习必备命令的使用

1.2 方案

准备2台虚拟机，要求如下：

IP地址	主机名	说明
192.168.88.50	MySQL 50	配置yum源，关闭selinux和防火墙
192.168.88.51	MySQL 51	配置yum源，关闭selinux和防火墙

1.3 步骤

实现此案例需要按照如下步骤进行。

步骤一：安装软件

命令操作如下所示：

mysql-server 提供服务软件

mysql 提供命令软件

[root@mysql50 ~]# yum -y install mysql-server  mysql  //安装提供服务和命令软件
//软件已安装
[root@mysql50 ~]# rpm -q mysql-server  mysql
mysql-server-8.0.26-1.module+el8.4.0+652+6de068a7.x86_64
mysql-8.0.26-1.module+el8.4.0+652+6de068a7.x86_64
[root@mysql50 ~]#
[root@mysql50 ~]# rpm -qi mysql-server  //查看软件信息
Name        : mysql-server
Version     : 8.0.26
Release     : 1.module+el8.4.0+652+6de068a7
Architecture: x86_64
Install Date: 2023年03月13日 星期一 12时09分38秒
Group       : Unspecified
Size        : 126674945
License     : GPLv2 with exceptions and LGPLv2 and BSD
Signature   : RSA/SHA256, 2021年09月22日 星期三 07时27分14秒, Key ID 15af5dac6d745a60
Source RPM  : mysql-8.0.26-1.module+el8.4.0+652+6de068a7.src.rpm
Build Date  : 2021年09月22日 星期三 07时06分32秒
Build Host  : ord1-prod-x86build005.svc.aws.rockylinux.org
Relocations : (not relocatable)
Packager    : [email protected]
Vendor      : Rocky
URL         : http://www.mysql.com
Summary     : The MySQL server and related files
Description :
MySQL is a multi-user, multi-threaded SQL database server. MySQL is a
client/server implementation consisting of a server daemon (mysqld)
and many different client programs and libraries. This package contains
the MySQL server and some accompanying files and directories.
[root@mysql50 ~]# systemctl  start  mysqld  //启动服务
[root@mysql50 ~]# systemctl  enable  mysqld  //开机运行
[root@mysql50 ~]# systemctl  enable mysqld  //设置服务开机运行
Created symlink /etc/systemd/system/multi-user.target.wants/mysqld.service → /usr/lib/systemd/system/mysqld.service.

步骤二：查看端口号和进程名

命令操作如下所示：

[root@mysql50 ~]# ps -C mysqld   //查看进程
    PID TTY          TIME CMD
  21912 ?        00:00:00 mysqld
[root@mysql50 ~]#
[root@mysql50 ~]# ss -utnlp  | grep 3306  查看端口
tcp   LISTEN 0      70                 *:33060            *:*    users:(("mysqld",pid=21912,fd=22))
tcp   LISTEN 0      128                *:3306             *:*    users:(("mysqld",pid=21912,fd=25))
[root@mysql50 ~]# 
或
[root@mysql50 ~]# netstat  -utnlp  | grep  mysqld   //仅查看mysqld进程
tcp6       0      0 :::33060   :::*      LISTEN      21912/mysqld        
tcp6       0      0 :::3306    :::*     LISTEN      21912/mysqld        
[root@mysql50 ~]#

说明：

MySQL 8中的3306端口是MySQL服务默认使用的端口，主要用于建立客户端与MySQL服务器之间的连接。

MySQL 8中的33060端口是MySQL Shell默认使用的管理端口，主要用于执行各种数据库管理任务。远程管理MySQL服务器：使用MySQL Shell连接到MySQL服务，并在远程管理控制台上执行各种数据库管理操作，例如创建、删除、备份和恢复数据库等。

步骤三：连接服务。

说明： 数据库管理员本机登陆默认没有密码

命令操作如下所示：

[root@mysql50 ~]# mysql  //连接服务
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.26 Source distribution
Copyright (c) 2000, 2021, 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>  登陆后的提示符
mysql> exit //断开连接
Bye
[root@mysql50 ~]#

步骤四：配置第2台数据库服务器MySQL51。

命令操作如下所示：

[root@mysql51 ~]# yum -y install  mysql-server mysql
[root@mysql51 ~]# systemctl  start mysqld
[root@mysql51 ~]# systemctl  enable mysqld
[root@mysql51 ~]# mysql
mysql> exit
Bye
[root@mysql51 ~]#

步骤五：练习必备命令的使用（在mysql50主机完成练习）

命令操作如下所示：

mysql> select version() ;  //查看数据库软件版本
+-----------+
| version() |
+-----------+
| 8.0.26    |
+-----------+
1 row in set (0.00 sec)
mysql> select user() ; //查看登陆的用户和客户端地址 
+----------------+
| user()         |
+----------------+
| root@localhost | 管理员root本机登陆
+----------------+
1 row in set (0.00 sec) 
mysql> show databases; //查看已有的库
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)
mysql>

说明：

默认4个库 不可以删除，存储的是 服务运行时加载的不同功能的程序和数据。

information_schema：是MySQL数据库提供的一个虚拟的数据库，存储了MySQL数据库中的相关信息，比如数据库、表、列、索引、权限、角色等信息。它并不存储实际的数据，而是提供了一些视图和存储过程，用于查询和管理数据库的元数据信息。

mysql：存储了MySQL服务器的系统配置、用户、账号和权限信息等。它是MySQL数据库最基本的库，存储了MySQL服务器的核心信息。

performance_schema：存储了MySQL数据库的性能指标、事件和统计信息等数据，可以用于性能分析和优化。

sys：是MySQL 8.0引入的一个新库，它基于information_schema和performance_schema视图，提供了更方便、更直观的方式来查询和管理MySQL数据库的元数据和性能数据。

mysql> select database();  //查看当前在那个库里  null 表示没有在任何库里
+------------+
| database() |
+------------+
| NULL       |
+------------+
1 row in set (0.00 sec)
mysql> use mysql ; //切换到mysql库
mysql> select database();  // 再次显示所在的库
+------------+
| database() |
+------------+
| mysql      |
+------------+
1 row in set (0.00 sec)
mysql> show tables;  //显示库里已有的表
+------------------------------------------------------+
| Tables_in_mysql                                      |
+------------------------------------------------------+
| columns_priv                                         |
| component                                            |
| db                                                   |
| default_roles                                        |
| engine_cost                                          |
| func                                                 |
| general_log                                          |
| global_grants                                        |
| gtid_executed                                        |
| help_category                                        |
| help_keyword                                         |
| help_relation                                        |
| help_topic                                           |
| innodb_index_stats                                   |
| innodb_table_stats                                   |
| password_history                                     |
| plugin                                               |
| procs_priv                                           |
| proxies_priv                                         |
| replication_asynchronous_connection_failover         |
| replication_asynchronous_connection_failover_managed |
| replication_group_configuration_version              |
| replication_group_member_actions                     |
| role_edges                                           |
| server_cost                                          |
| servers                                              |
| slave_master_info                                    |
| slave_relay_log_info                                 |
| slave_worker_info                                    |
| slow_log                                             |
| tables_priv                                          |
| time_zone                                            |
| time_zone_leap_second                                |
| time_zone_name                                       |
| time_zone_transition                                 |
| time_zone_transition_type                            |
| user                                                 |
+------------------------------------------------------+
37 rows in set (0.00 sec)
mysql> exit ;  断开连接
Bye
[root@mysql50 ~]#  

2 案例2：密码管理

2.1 问题

1） 在192.168.88.50主机做如下练习：

1. 设置root密码为tarena
2. 修改root密码为123qqq…A
3. 破解root密码为NSD2023…a

2.2 步骤

实现此案例需要按照如下步骤进行。

步骤一：设置root密码为tarena

命令操作如下所示：

2行输出是警告而已不用关心

[root@mysql50 ~]# mysqladmin  -uroot -p  password "tarena"
Enter password: //敲回车
mysqladmin: [Warning] Using a password on the command line interface can be insecure.
Warning: Since password will be sent to server in plain text, use ssl connection to ensure password safety.
 [root@mysql50 ~]# mysql //无密码连接被拒绝
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
[root@mysql50 ~]#
[root@mysql50 ~]# mysql -uroot –ptarena  //连接时输入密码
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 14
Server version: 8.0.26 Source distribution
Copyright (c) 2000, 2021, 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> 登陆成功

步骤二：修改root密码为123qqq…A

命令操作如下所示：

[root@mysql50 ~]# mysqladmin  -uroot -ptarena password "123qqq...A"  //修改密码
mysqladmin: [Warning] Using a password on the command line interface can be insecure.
Warning: Since password will be sent to server in plain text, use ssl connection to ensure password safety.
[root@mysql50 ~]# mysql -uroot –ptarena //旧密码无法登陆
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
[root@mysql50 ~]# mysql -uroot -p123qqq...A  //新密码登陆
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 18
Server version: 8.0.26 Source distribution
Copyright (c) 2000, 2021, 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> 登陆成功

步骤三：破解root密码为NSD2023…a

说明：在mysql50主机做此练习

命令操作如下所示：

[root@mysql50 ~]# mysql -uroot -pNSD2023...a  //破解前登陆失败
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
[root@mysql50 ~]# vim /etc/my.cnf.d/mysql-server.cnf  //修改主配置文件
[mysqld]
skip-grant-tables  //手动添加此行 作用登陆时不验证密码
:wq
[root@mysql50 ~]# systemctl  restart mysqld //重启服务 作用让服务以新配置运行
[root@mysql50 ~]# mysql //连接服务
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 7
Server version: 8.0.26 Source distribution
Copyright (c) 2000, 2021, 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.
//把mysql库下user表中 用户root的密码设置为无；
mysql> update mysql.user set authentication_string="" where user="root";
Query OK, 1 row affected (0.05 sec)
Rows matched: 1  Changed: 1  Warnings: 0
mysql> exit; 断开连接
Bye
 [root@mysql50 ~]# vim  /etc/my.cnf.d/mysql-server.cnf  编辑配置文件
[mysqld]
#skip-grant-tables   //注释添加的行
:wq
[root@mysql50 ~]# systemctl  restart mysqld //重启服务 作用让注释生效
[root@localhost ~]# mysql  无密码登陆
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.26 Source distribution
Copyright (c) 2000, 2021, 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.
//设置root用户本机登陆密码
mysql> alter user root@"localhost" identified by "NSD2023...a";
Query OK, 0 rows affected (0.00 sec)
mysql> exit 断开连接
Bye
[root@localhost ~]# mysql  不输密码无法登陆
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
[root@localhost ~]# mysql -uroot -pNSD2023...a  使用破解的密码登陆
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 10
Server version: 8.0.26 Source distribution
Copyright (c) 2000, 2021, 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>
mysql> 登陆成功
mysql> show databases; 查看已有的库
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.01 sec)

3 案例3：安装图形软件

3.1 问题

• 在IP地址192.168.88.50主机安装phpmyadmin软件
• 客户端通过访问phpmyadmin软件管理数据库

3.2 方案

把用到的软件拷贝的虚拟机mysql50里

在mysql50主机，首先配置运行环境LNP,然后安装phpmyadmin软件,最后打开真机的浏览器输入phpmyadmin的网址访问。

3.3 步骤

实现此案例需要按照如下步骤进行。

步骤一：部署运行环境LNP

命令操作如下所示：

gcc 源码包编译工具
unzip 提供解压.zip 压缩包命令
make 源码软件编译命令
pcre-devel 支持正则表达式
zlib-devel 提供数据压缩命令
[root@mysql50 ~]# yum -y install gcc unzip make pcre-devel zlib-devel //安装依赖
[root@mysql50 ~]# tar -xf nginx-1.22.1.tar.gz //解压源码
[root@mysql50 ~]# cd nginx-1.22.1 //进源码目录
[root@mysql50 nginx-1.22.1]# ./configure //配置
[root@mysql50 nginx-1.22.1]# make &&  make  install //编译并安装
[root@mysql50 nginx-1.22.1]# ls /usr/local/nginx/   //查看安装目录
conf  html  logs  sbin
[root@mysql50 nginx-1.22.1]# vim /usr/local/nginx/conf/nginx.conf //修改主配置文件
43         location / {
44             root   html;
45             index  index.php index.html index.htm; //添加php首页名
46         }
65         location ~ \.php$ {  //访问.php的请求转给本机的9000端口
66             root           html;
67             fastcgi_pass   127.0.0.1:9000;
68             fastcgi_index  index.php;
69            #fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
70             include        fastcgi.conf;  //保存nginx变量文件
71         }
:wq
[root@mysql50 nginx-1.22.1]# /usr/local/nginx/sbin/nginx //启动服务
[root@mysql50 nginx-1.22.1]# netstat  -utnlp  | grep 80  //查看端口
tcp        0      0 0.0.0.0:80     0.0.0.0:*     LISTEN      42182/nginx: master 
[root@mysql50 nginx-1.22.1]#
php 解释php代码
php-devel php扩展包 
php-mysqlnd 连接mysql命令包
php-json 支持json代码
php-fpm 提供fpm服务
[root@mysql50 ~]# yum -y install php  php-devel php-mysqlnd php-json php-fpm //安装php软件
[root@mysql50 ~]# vim /etc/php-fpm.d/www.conf //修改主配置文件
38 ;listen = /run/php-fpm/www.sock
39 listen = 127.0.0.1:9000  //非socket方式运行,不是必须的
:wq
[root@mysql50 ~]# systemctl  start php-fpm  //启动服务
[root@mysql50 ~]# netstat  -utnlp  | grep 9000  //查看端口
tcp        0      0 127.0.0.1:9000     0.0.0.0:*    LISTEN    67251/php-fpm: mast 
[root@mysql50 ~]#
[root@mysql50 ~]# vim /usr/local/nginx/html/test.php //编写php脚本

:wq
[root@mysql50 ~]# curl  http://localhost/test.php  //访问脚本
plj
[root@mysql50 ~]#

步骤二：安装phpmyadmin软件

命令操作如下所示：

[root@mysql50 ~]# unzip phpMyAdmin-5.2.1-all-languages.zip  //解压
[root@mysql50 ~]# mv phpMyAdmin-5.2.1-all-languages /usr/local/nginx/html/phpmyadmin  //移动并改名 ，为了便于访问
[root@mysql50 ~]# cd /usr/local/nginx/html/phpmyadmin/  //进软件目录
[root@mysql50 phpmyadmin]# cp config.sample.inc.php config.inc.php //创建主配置文件
[root@mysql50 phpmyadmin]# vim config.inc.php //修改主配置文件
//定义cookies验证码
16 $cfg['blowfish_secret'] = 'plj123'; /* YOU MUST FILL IN THIS FOR COOKIE AUTH! */
//管理本机的数据库服务
30 $cfg['Servers'][$i]['host'] = 'localhost';
:wq
[root@mysql50 phpmyadmin]# setenforce 0  //关闭selinux
[root@mysql50 phpmyadmin]# systemctl  stop firewalld //关闭防火墙

步骤三：客户端访问

命令操作如下所示：

http://192.168.88.50/phpmyadmin 打开浏览器输入此网址 效果如图所示

 说明：输入数据库管理员root 和 密码 成功后如图所示

4 案例4：筛选条件

4.1 问题

1. 准备练习环境
2. 练习数值比较
3. 练习范围匹配
4. 练习模糊匹配
5. 练习正则匹配
6. 练习逻辑比较
7. 练习字符比较/空/非空
8. 练习别名/去重/合并

4.2 方案

拷贝tarena.sql文件到mysql50主机里，然后使用tarena.sql创建练习使用的数据。

4.3 步骤

实现此案例需要按照如下步骤进行。

步骤一：准备练习环境

//拷贝tarena.sql 拷贝到 mysql50主机的/root 下
[openeuler@server1 ~]$ scp /linux-soft/s3/tarena.sql  [email protected]:/root/
[email protected]'s password: 
tarena.sql    100%  284KB 171.9MB/s   00:00 
//连接mysql50主机                                                                                    
[openeuler@server1 ~]$ ssh [email protected]
[email protected]'s password: 
Last login: Tue May 23 10:59:57 2023 from 192.168.88.254
//恢复数据
[root@mysql50 ~]# mysql -uroot  -pNSD2023...a < /root/tarena.sql
mysql: [Warning] Using a password on the command line interface can be insecure.
//连接服务
[root@mysql50 ~]# mysql -uroot  -pNSD2023...a
mysql> show databases; //查看库
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| tarena             | 恢复的库
+--------------------+
5 rows in set (0.00 sec)
mysql> use tarena; //进入库
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
mysql> show tables;  //查看表
+------------------+
| Tables_in_tarena |
+------------------+
| departments      | 部门表
| employees        | 员工表
| salary           | 工资表
| user             | 用户表
+------------------+
4 rows in set (0.00 sec)

使用user 表做查询练习

user表里存储的是 系统用户信息 就是 /etc/passwd 文件的内容

mysql> desc tarena.user;  //查看表头
+----------+-------------+------+-----+---------+----------------+
| Field    | Type        | Null | Key | Default | Extra          |
+----------+-------------+------+-----+---------+----------------+
| id       | int(11)     | NO   | PRI | NULL    | auto_increment |行号
| name     | char(20)    | YES  |     | NULL    |                  |用户名
| password | char(1)     | YES  |     | NULL    |                  |密码占位符
| uid      | int(11)     | YES  |     | NULL    |                  | uid号
| gid      | int(11)     | YES  |     | NULL    |                  | gid号
| comment  | varchar(50) | YES  |     | NULL    |                 | 描述信息
| homedir  | varchar(80) | YES  |     | NULL    |                 | 家目录
| shell    | char(30)    | YES  |     | NULL    |                  | 解释器
+----------+-------------+------+-----+---------+----------------+
8 rows in set (0.00 sec)

select命令格式演示

语法格式1 SELECT 字段列表 FROM 库名.表名;

语法格式2 SELECT 字段列表 FROM 库名.表名 where 筛选条件;

mysql> select name from  tarena.user;        //查看一个表头
mysql> select name ,uid from  tarena.user;    //查看多个表头
mysql> select *  from  tarena.user;        //查看所有表头

加筛选条件

mysql> select *  from  tarena.user where  name = “root”;        //查找root用户信息 
+----+------+----------+------+------+---------+---------+-----------+
| id | name | password | uid  | gid  | comment | homedir | shell     |
+----+------+----------+------+------+---------+---------+-----------+
|  1 | root | x        |    0 |    0 | root    | /root   | /bin/bash |
+----+------+----------+------+------+---------+---------+-----------+
1 row in set (0.00 sec)
mysql> 
mysql> select *  from  tarena.user where  id = 2 ;        //查找第2行用户信息
+----+------+----------+------+------+---------+---------+--------------+
| id | name | password | uid  | gid  | comment | homedir | shell         |
+----+------+----------+------+------+---------+---------+--------------+
|  2 | bin   | x        |    1 |   1   | bin      | /bin   | /sbin/nologin |
+----+------+----------+------+------+---------+---------+--------------+
1 row in set (0.00 sec)

步骤二：练习数值比较

比较符号：

= != > >= < <=

相等 不相等 大于 大于等于 小于 小于等于

符号两边要是数字或数值类型的表头 符号左边与符号右边做比较

//查看第3行的行号、用户名、uid、gid  四个表头的值
mysql> select  id,name,uid,gid  from  tarena.user where  id = 3;
+----+--------+------+------+
| id | name   | uid  | gid  |
+----+--------+------+------+
|  3 | daemon |    2 |    2 |
+----+--------+------+------+
1 row in set (0.00 sec)
//查看前2行的行号用户名、uid、gid 四个表头的值
mysql> select  id,name,uid,gid  from  tarena.user where  id < 3;
+----+------+------+------+
| id | name | uid  | gid  |
+----+------+------+------+
|  1 | root |    0 |    0 |
|  2 | bin  |    1 |    1 |
+----+------+------+------+
2 rows in set (0.00 sec)
//查看前3行的行号、用户名、uid、gid  四个表头的值
mysql> select  id,name,uid,gid  from  tarena.user where  id <= 3;
+----+--------+------+------+
| id | name   | uid  | gid  |
+----+--------+------+------+
|  1 | root   |    0 |    0 |
|  2 | bin    |    1 |    1 |
|  3 | daemon |    2 |    2 |
+----+--------+------+------+
3 rows in set (0.00 sec)
//查看前uid号大于6000的行号、用户名、uid、gid  四个表头的值
mysql> select  id,name,uid,gid  from  tarena.user where  uid > 6000;
+----+-----------+-------+-------+
| id | name      | uid   | gid   |
+----+-----------+-------+-------+
| 22 | nfsnobody | 65534 | 65534 |
+----+-----------+-------+-------+
1 row in set (0.00 sec)
//查看前uid号大于等于1000的行号、用户名、uid、gid  四个表头的值
mysql> select  id,name,uid,gid  from  tarena.user where  uid >= 1000;
+----+-----------+-------+-------+
| id | name      | uid   | gid   |
+----+-----------+-------+-------+
| 22 | nfsnobody | 65534 | 65534 |
| 24 | plj       |  1000 |  1000 |
+----+-----------+-------+-------+
2 rows in set (0.00 sec)
//查看uid号和gid号相同的行 仅显示行号、用户名、uid、gid  四个表头的值
mysql> select  id,name,uid,gid  from  tarena.user where  uid = gid;
+----+-----------------+-------+-------+
| id | name            | uid   | gid   |
+----+-----------------+-------+-------+
|  1 | root            |     0 |     0 |
|  2 | bin             |     1 |     1 |
|  3 | daemon          |     2 |     2 |
| 13 | nobody          |    99 |    99 |
| 14 | systemd-network |   192 |   192 |
| 15 | dbus            |    81 |    81 |
| 17 | sshd            |    74 |    74 |
| 18 | postfix         |    89 |    89 |
| 20 | rpc             |    32 |    32 |
| 21 | rpcuser         |    29 |    29 |
| 22 | nfsnobody       | 65534 | 65534 |
| 23 | haproxy         |   188 |   188 |
| 24 | plj             |  1000 |  1000 |
| 25 | apache          |    48 |    48 |
| 26 | mysql           |    27 |    27 |
+----+-----------------+-------+-------+
15 rows in set (0.00 sec)
//查看uid号和gid号不一样的行 仅显示行号、用户名、uid、gid  四个表头的值
mysql> select  id,name,uid,gid  from  tarena.user where  uid != gid;
+----+----------+------+------+
| id | name     | uid  | gid  |
+----+----------+------+------+
|  4 | adm      |    3 |    4 |
|  5 | lp       |    4 |    7 |
|  6 | sync     |    5 |    0 |
|  7 | shutdown |    6 |    0 |
|  8 | halt     |    7 |    0 |
|  9 | mail     |    8 |   12 |
| 10 | operator |   11 |    0 |
| 11 | games    |   12 |  100 |
| 12 | ftp      |   14 |   50 |
| 16 | polkitd  |  999 |  998 |
| 19 | chrony   |  998 |  996 |
+----+----------+------+------+
11 rows in set (0.00 sec)
mysql>

步骤三：练习范围匹配

in （值列表） //在…里

not in （值列表） //不在…里

between 数字1 and 数字2 //在…之间

命令操作如下所示：

//uid号表头的值 是 (1 , 3 , 5 , 7) 中的任意一个即可
mysql> select name , uid  from  tarena.user where  uid  in (1 , 3 , 5 , 7);  
+------+------+
| name | uid  |
+------+------+
| bin  |    1 |
| adm  |    3 |
| sync |    5 |
| halt |    7 |
+------+------+
//shell 表头的的值 不是 "/bin/bash"或"/sbin/nologin" 即可
mysql> select name , shell  from  tarena.user where  shell  not in ("/bin/bash","/sbin/nologin");
+----------+----------------+
| name     | shell          |
+----------+----------------+
| sync     | /bin/sync      |
| shutdown | /sbin/shutdown |
| halt     | /sbin/halt     |
| mysql    | /bin/false     |
+----------+----------------+
//id表头的值 在 10  到  20 之间即可 包括 10 和  20  本身
mysql> select id , name , uid  from  tarena.user where id  between 10 and 20 ;
+----+-----------------+------+
| id | name            | uid  |
+----+-----------------+------+
| 10 | operator        |   11 |
| 11 | games           |   12 |
| 12 | ftp             |   14 |
| 13 | nobody          |   99 |
| 14 | systemd-network |  192 |
| 15 | dbus            |   81 |
| 16 | polkitd         |  999 |
| 17 | sshd            |   74 |
| 18 | postfix         |   89 |
| 19 | chrony          |  998 |
| 20 | rpc             |   32 |
+----+-----------------+------+
11 rows in set (0.00 sec)mysql> 

步骤四：练习模糊匹配

where 字段名 like "表达式";

通配符

_ 表示 1个字符

% 表示零个或多个字符

命令操作如下所示：

//找名字必须是3个字符的 （没有空格挨着敲）
mysql> select name from  tarena.user where  name like "___"; 
+------+
| name |
+------+
| bin  |
| adm  |
| ftp  |
| rpc  |
| plj  |
| bob  |
+------+
6 rows in set (0.00 sec)
//找名字必须是4个字符的（没有空格挨着敲）
mysql> select name from  tarena.user where  name like "_ _ _ _"; 
+------+
| name |
+------+
| root |
| sync |
| halt |
| mail |
| dbus |
| sshd |
| null |
+------+
7 rows in set (0.00 sec)
//找名字以字母a开头的（没有空格挨着敲）
mysql> select name from  tarena.user where  name like "a%";  
//查找名字至少是4个字符的表达式
mysql> select name from  tarena.user where  name like "%_ _ _ _%";（没有空格挨着敲）
mysql> select name from  tarena.user where name  like "_ _%_ _";（没有空格挨着敲）
mysql> select name from  tarena.user where name  like "_ _ _ _%";（没有空格挨着敲）

步骤五：练习正则匹配

格式：select 字段名列表 from 库名.表名 where字段名 regexp '正则表达式'；

回顾shell课程学过的元字符(正则符号)

^ 匹配行首

$ 匹配行尾

[] 匹配范围内任意一个

* 前边的表达式出现零次或多次

| 或者

. 任意一个字符

命令操作如下所示：

//添加有数字的名字
insert into  tarena.user(name)values("yaya9");
insert into  tarena.user(name)values("6yaya");
insert into  tarena.user(name)values("ya7ya");
insert into  tarena.user(name)values("yay8a");
//查看名字里有数字的
mysql> select name from  tarena.user where name regexp "[0-9]"; 
+-------+
| name  |
+-------+
| yaya9 |
| 6yaya |
| ya7ya |
| yay8a |
+-------+
4 rows in set (0.00 sec)
//查看名字以数字开头
mysql> select name from  tarena.user where name regexp "^[0-9]"; 
+-------+
| name  |
+-------+
| 6yaya |
+-------+
1 row in set (0.00 sec)
//查看名字以数字结尾
mysql> select name from  tarena.user where name regexp "[0-9]$"; 
+-------+
| name  |
+-------+
| yaya9 |
+-------+
1 row in set (0.00 sec)
mysql> 
//查看名字以r开头
mysql> select name from  tarena.user where name regexp "^r"; 
+---------+
| name    |
+---------+
| root    |
| rpc     |
| rpcuser |
+---------+
3 rows in set (0.00 sec)
//查看名字以t结尾
mysql> select name from  tarena.user where name regexp "t$"; 
+------+
| name |
+------+
| root |
| halt |
+------+
2 rows in set (0.00 sec)
mysql> 
//查看名字以r开头或t结尾
mysql> select name from  tarena.user where name regexp "^r|t$"; 
+---------+
| name    |
+---------+
| root    |
| halt    |
| rpc     |
| rpcuser |
+---------+
4 rows in set (0.00 sec)
//名字r开头t结尾
mysql> select name from  tarena.user where name regexp "^r.*t$"; 
+------+
| name |
+------+
| root |
+------+
1 row in set (0.00 sec)
mysql> 

步骤六：练习逻辑比较

多个判断条件

逻辑与 and （&&） 多个判断条件必须同时成立

逻辑或 or （||） 多个判断条件其中某个条件成立即可

逻辑非 not （!） 取反

命令操作如下所示：

//逻辑非例子，查看解释器不是/bin/bash 的
mysql> select name,shell from tarena.user where  shell != "/bin/bash"; 
//not 也是取反  要放在表达式的前边
mysql> select name,shell from tarena.user where  not  shell = "/bin/bash";
//id值不在 10 到 20 之间 
mysql> select id , name from tarena.user where not  id between 10 and 20 ;  
//逻辑与 例子
mysql> select name , uid from tarena.user where name="root" and uid = 1;      
Empty set (0.00 sec)
mysql> select name , uid from tarena.user where name="root" and uid = 0;
+------+------+
| name | uid  |
+------+------+
| root |    0 |
+------+------+
1 row in set (0.00 sec)
//逻辑或 例子
mysql> select name , uid from tarena.user where name = "root"  or  name = "bin"  or  uid = 1;
+------+------+
| name | uid  |
+------+------+
| root |    0 |
| bin  |    1 |
+------+------+
mysql>

() 提高优先级

mysql> select   2  + 3 * 5 ; //使用默认计算顺序 先乘除后加减
+------------+
| 2  + 3 * 5 |
+------------+
|         17 |
+------------+
1 row in set (0.00 sec)
mysql> select   (2  + 3 ) * 5 ; //先加法再乘法
+---------------+
| (2  + 3 ) * 5 |
+---------------+
|            25 |
+---------------+
1 row in set (0.00 sec)
mysql>

逻辑匹配什么时候需要加（）

逻辑与and 优先级高于逻辑或 or

如果在筛选条件里既有and 又有 or 默认先判断and 再判断or

//没加（） 的查询结果
select name , uid from tarena.user  
where name = "root" or name = "bin"  and uid = 1 ;  
+------+------+
| name | uid  |
+------+------+
| root |    0 |
| bin  |    1 |
+------+------+
2 rows in set (0.00 sec)
//加（）的查询结果
select name , uid from tarena.user  
where (name = "root" or name = "bin")  and uid = 1 ;  
+------+------+
| name | uid  |
+------+------+
| bin  |    1 |
+------+------+
1 row in set (0.00 sec)
mysql>

步骤七：练习字符比较/空/非空

符号两边必须是字符 或字符类型的表头

= 相等比较

!= 不相等比较。

命令操作如下所示：

//查看表里是否有名字叫apache的用户
mysql> select  name  from  tarena.user where name="apache" ;
+--------+
| name   |
+--------+
| apache |
+--------+
1 row in set (0.00 sec)
//输出解释器不是/bin/bash的用户名 及使用的解释器
mysql> select  name , shell  from  tarena.user where shell != "/bin/bash";
+-----------------+----------------+
| name            | shell          |
+-----------------+----------------+
| bin             | /sbin/nologin  |
| daemon          | /sbin/nologin  |
| adm             | /sbin/nologin  |
| lp              | /sbin/nologin  |
| sync            | /bin/sync      |
| shutdown        | /sbin/shutdown |
| halt            | /sbin/halt     |
| mail            | /sbin/nologin  |
| operator        | /sbin/nologin  |
| games           | /sbin/nologin  |
| ftp             | /sbin/nologin  |
| nobody          | /sbin/nologin  |
| systemd-network | /sbin/nologin  |
| dbus            | /sbin/nologin  |
| polkitd         | /sbin/nologin  |
| sshd            | /sbin/nologin  |
| postfix         | /sbin/nologin  |
| chrony          | /sbin/nologin  |
| rpc             | /sbin/nologin  |
| rpcuser         | /sbin/nologin  |
| nfsnobody       | /sbin/nologin  |
| haproxy         | /sbin/nologin  |
| apache          | /sbin/nologin  |
| mysql           | /bin/false     |
+-----------------+----------------+
24 rows in set (0.00 sec)
mysql>

空 is null 表头下没有数据

非空 is not null 表头下有数据

mysql服务 使用关键字 null 或 NULL 表示表头没有数据

//添加新行 仅给行中的id 表头和name表头赋值
mysql> insert into tarena.user(id,name) values(71,"");    //零个字符
mysql> insert into tarena.user(id,name) values(72,"null");//普通字母
mysql> insert into tarena.user(id,name) values(73,NULL);  //表示空
mysql> insert into tarena.user(id,name) values(74,null);  //表示空
//查看id表头值大于等于70  的行 仅显示行中 id表头 和  name 表头的值
mysql> select id , name from  tarena.user where  id >= 71;
+----+------+
| id | name |
+----+------+
| 71 |      |
| 72 | null |
| 73 | NULL |
| 74 | NULL |
+----+------+
//查看name 表头没有数据的行 仅显示行中id表头 和  naeme 表头的值
mysql> select id , name from  tarena.user where name is null;
+----+------+
| id | name |
+----+------+
| 28 | NULL |
| 29 | NULL |
| 73 | NULL |
| 74 | NULL |
+----+------+
//查看name 表头是0个字符的行， 仅显示行中id表头 和  naeme 表头的值
mysql> select id , name from  tarena.user where name="";
+----+------+
| id | name |
+----+------+
| 71 |      |
+----+------+
1 row in set (0.00 sec)
//查看name 表头值是null的行， 仅显示行中id表头 和  naeme 表头的值
mysql> select id , name from  tarena.user where name="null";
+----+------+
| id | name |
+----+------+
| 72 | null |
+----+------+
1 row in set (0.00 sec)
//查看name 表头有数据的行， 仅显示行中id表头 和  name 表头的值
mysql> select id , name from  tarena.user where name is not null;
+----+-----------------+
| id | name            |
+----+-----------------+
|  1 | root            |
|  2 | bin             |
|  3 | daemon          |
|  4 | adm             |
|  5 | lp              |
....
....
| 27 | bob             |
| 71 |                 |
| 72 | null            |
+----+-----------------+

步骤八：练习别名/去重/合并

命令操作如下所示：

//定义别名使用   as  或  空格    
mysql> select name , homedir  from tarena.user;
mysql> select name as 用户名 , homedir  家目录 from tarena.user;
//拼接   concat()
mysql> select concat(name,"-",uid) as 用户信息 from tarena.user where uid <= 5;
+--------------+
| 用户信息     |
+--------------+
| root-0       |
| bin-1        |
| daemon-2     |
| adm-3        |
| lp-4         |
| sync-5       |
+--------------+
6 rows in set (0.00 sec)
//2列拼接
mysql>  select concat(name , "-" , uid)  as  用户信息  from tarena.user where uid <= 5;
//多列拼接
mysql>  select concat(name , "-" , uid , "-" , gid)  as  用户信息  from tarena.user where uid <= 5;
+--------------+
| 用户信息     |
+--------------+
| root-0-0     |
| bin-1-1      |
| daemon-2-2   |
| adm-3-4      |
| lp-4-7       |
| sync-5-0     |
+--------------+

去重显示 distinct 字段名列表

//去重前输出
mysql> select shell  from  tarena.user  where shell in ("/bin/bash","/sbin/nologin") ;
+---------------+
| shell         |
+---------------+
| /bin/bash     |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /sbin/nologin |
| /bin/bash     |
| /sbin/nologin |
+---------------+
22 rows in set (0.00 sec)
//去重后查看
mysql> select distinct shell  from  tarena.user  where shell in ("/bin/bash","/sbin/nologin") ;
+---------------+
| shell         |
+---------------+
| /bin/bash     |
| /sbin/nologin |
+---------------+
2 rows in set (0.01 sec)
mysql>