本文介绍在centos-7下安装、卸载mysql 8.0，并使用SQLyog客户端工具连接mysql.
1. 卸载MySQL
1.1 卸载mariadb
检查mariadb: $ rpm -qa|grep mariadb
如果上面检查的结果有内容，则删除mariadb，把命令中的mariadb-server替换成所有上面输出的内容: $ rpm \-e --nodeps mariadb-server
1.2 卸载mysql
检查mysql:
$ rpm -qa|grep mysql
mysql80-community-release-el7-3.noarch
mysql-community-libs-8.0.19-1.el7.x86_64
mysql-community-server-8.0.19-1.el7.x86_64
mysql-community-common-8.0.19-1.el7.x86_64
mysql-community-client-8.0.19-1.el7.x86_64$ systemctl status mysqld
● mysqld.service - MySQL Server
Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
Active: active (running) since Sat 2020-04-04 15:46:48 CST; 6 days ago
Docs: man:mysqld(8)
http://dev.mysql.com/doc/refman/en/using-systemd.html
Main PID: 9608 (mysqld)
Status: "Server is operational"
CGroup: /system.slice/mysqld.service
└─9608 /usr/sbin/mysqld停止mysqld.service服务：$ sudo systemctl stop mysqld
删除mysql程序：
$ sudo rpm -e --nodeps mysql80-community-release-el7-3.noarch mysql-community-libs-8.0.19-1.el7.x86_64 mysql-community-server-8.0.19-1.el7.x86_64 mysql-community-common-8.0.19-1.el7.x86_64 mysql-community-client-8.0.19-1.el7.x86_64
warning: /etc/my.cnf saved as /etc/my.cnf.rpmsave删除所有mysql相关文件：$ sudo rm -rf /var/lib/mysql /var/log/mysqld.log
2. 安装MySQL
在CentOS-7中安装MySQL需要配置下载源，不能直接使用yum安装
2.1 添加MySQL Yum Repository
下载MySQL源
查看系统版本：
shell> cat /etc/redhat-release
CentOS Linux release 7.6.1810 (Core)选择对应的版本进行下载，例如CentOS 7当前在官网查看最新Yum源的下载地址为： dev.mysql.com/get/mysql80…
shell> wget https://dev.mysql.com/get/mysql80-community-release-el7-3.noarch.rpm安装MySQL源
shell> sudo rpm -Uvh platform-and-version-specific-package-name.rpm例如CentOS7当前最新MySQL源安装： shell> sudo rpm -Uvh mysql80-community-release-el7-3.noarch.rpm
检查是否安装成功
执行成功后会在/etc/yum.repos.d/目录下生成两个repo文件mysql-community.repo及 mysql-community-source.repo
并且通过yum repolist可以看到mysql相关资源
shell> yum repolist enabled | grep "mysql.*-community.*"
!mysql-connectors-community/x86_64 MySQL Connectors Community 108
!mysql-tools-community/x86_64 MySQL Tools Community 90
!mysql80-community/x86_64 MySQL 8.0 Community Server 1132.2 选择MySQL版本
使用MySQL Yum Repository安装MySQL，默认会选择当前最新的稳定版本，例如通过上面的MySQL源进行安装的话，默安装会选择MySQL 8.0版本，如果就是想要安装该版本，可以直接跳过此步骤，如果不是，比如我这里希望安装MySQL5.7版本，就需要“切换一下版本”：
查看当前MySQL Yum Repository中所有MySQL版本（每个版本在不同的子仓库中）
shell> yum repolist all | grep mysql切换版本
shell> sudo yum-config-manager --disable mysql80-community
shell> sudo yum-config-manager --enable mysql57-community2.3 安装MySQL
安装：$ sudo yum install mysql-community-server
启动：$ sudo systemctl start mysqld
查看状态：$ sudo systemctl status mysqld
2.4 设置root密码
我们自己进行测试时使用的root密码不必太复杂，通过设置my.cnf，可以设置简单密码（对mysql 8.0适用），设置完这些策略之后，必须执行sudo systemctl restart mysqld，才可使之生效：
validate_password.check_user_name = 0
validate_password.policy = 0
validate_password.mixed_case_count = 0
validate_password.number_count = 0
validate_password.special_char_count = 0
validate_password.length = 0查看mysql root用户的密码：
$ sudo grep 'temporary password' /var/log/mysqld.log
2020-04-12T12:06:54.577571Z 5 [Note] [MY-010454] [Server] A temporary password is generated for root@localhost: d%tcKY,VO6:o登录mysql:
$ mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.19
Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.
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> 修改默认root密码：
mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'root';
Query OK, 0 rows affected (0.01 sec)查看密码策略：
mysql> SHOW VARIABLES LIKE 'validate_password%';
+--------------------------------------+-------+
| Variable_name | Value |
+--------------------------------------+-------+
| validate_password.check_user_name | OFF |
| validate_password.dictionary_file | |
| validate_password.length | 0 |
| validate_password.mixed_case_count | 0 |
| validate_password.number_count | 0 |
| validate_password.policy | LOW |
| validate_password.special_char_count | 0 |
+--------------------------------------+-------+
7 rows in set (0.00 sec)2.5 允许远程连接
设置权限，允许远程连接root用户
mysql> CREATE USER 'root'@'%' IDENTIFIED BY 'root';
Query OK, 0 rows affected (0.01 sec)
mysql> GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' WITH GRANT OPTION;
Query OK, 0 rows affected (0.00 sec)设置加密方式，是SQLyog可以链接
mysql> ALTER USER 'root'@'%' IDENTIFIED WITH mysql_native_password BY 'root';
Query OK, 0 rows affected (0.00 sec)2.6 打开3306端口
$ sudo firewall-cmd --zone=public --add-port=3306/tcp --permanent
[sudo] password for eric:
success
$ sudo firewall-cmd --list-ports
$ sudo firewall-cmd --reload
success
$ sudo firewall-cmd --list-ports
3306/tcp3. 客户端SQLyog连接MySQL
使用SQLyog连接mysql即可