1. 首先，查看系统是否已经安装了mysql数据库

rpm -qa | grep mysql

演示如下：

[root@localhost etc]# rpm -qa | grep mysql
mysql-community-libs-8.0.16-2.el7.x86_64
mysql-community-common-8.0.16-2.el7.x86_64
mysql-community-client-8.0.16-2.el7.x86_64
mysql80-community-release-el7-3.noarch
mysql-community-server-8.0.16-2.el7.x86_64

2. 查询到已安装的MySQL库后，执行以下命令依次卸载

yum remove mysql-xxx-xxx

若没有查询后，没有安装Mysql库，可直接跳过此步。

3. 删除mysql的配置文件（MySQL卸载不会自动删除配置文件，需自行清理）

首先使用如下命令查找出所用的配置文件
find / -name mysql

[root@localhost etc]# find / -name mysql
/etc/logrotate.d/mysql
/var/lib/docker/overlay2/a74267a6cde69551beede82788b48f1430f6ac88e4c7a8cdf9bcf16b2125aac6/diff/etc/mysql
/var/lib/docker/overlay2/a74267a6cde69551beede82788b48f1430f6ac88e4c7a8cdf9bcf16b2125aac6/diff/usr/include/mysql
/var/lib/docker/overlay2/a74267a6cde69551beede82788b48f1430f6ac88e4c7a8cdf9bcf16b2125aac6/diff/usr/include/mysql/mysql
/var/lib/mysql
/var/lib/mysql/mysql
/usr/bin/mysql
/usr/lib64/mysql

根据需求使用以下命令 依次 对配置文件进行删除

rm -rf /var/lib/mysql

由于 在CentOS中默认安装有MariaDB，所以如果我们不删除MariaDB文件的话，安装mysql时可能会发生冲突。冲突信息如下：

[root@localhost yum.repos.d]# yum install mysql-community-server.x86_64 
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
 * base: mirrors.btte.net
 * epel: mirrors.ustc.edu.cn
 * extras: mirrors.163.com
 * updates: centos.ustc.edu.cn
Resolving Dependencies
--> Running transaction check
---> Package mariadb-server.x86_64 1:5.5.52-1.el7 will be obsoleted
--> Processing Dependency: mariadb-server for package: akonadi-mysql-1.9.2-4.el7.x86_64
---> Package mysql-community-server.x86_64 0:5.7.19-1.el7 will be obsoleting
--> Processing Dependency: mysql-community-common(x86-64) = 5.7.19-1.el7 for package: mysql-community-server-5.7.19-1.el7.x86_64
--> Processing Dependency: mysql-community-client(x86-64) >= 5.7.9 for package: mysql-community-server-5.7.19-1.el7.x86_64
--> Running transaction check
---> Package mariadb.x86_64 1:5.5.52-1.el7 will be obsoleted
---> Package mariadb-server.x86_64 1:5.5.52-1.el7 will be obsoleted
--> Processing Dependency: mariadb-server for package: akonadi-mysql-1.9.2-4.el7.x86_64
---> Package mysql-community-client.x86_64 0:5.7.19-1.el7 will be obsoleting
--> Processing Dependency: mysql-community-libs(x86-64) >= 5.7.9 for package: mysql-community-client-5.7.19-1.el7.x86_64
---> Package mysql-community-common.x86_64 0:5.7.19-1.el7 will be installed
--> Running transaction check
---> Package mariadb-libs.x86_64 1:5.5.52-1.el7 will be obsoleted
--> Processing Dependency: libmysqlclient.so.18()(64bit) for package: perl-DBD-MySQL-4.023-5.el7.x86_64
--> Processing Dependency: libmysqlclient.so.18()(64bit) for package: 2:postfix-2.10.1-6.el7.x86_64
--> Processing Dependency: libmysqlclient.so.18()(64bit) for package: 1:qt-mysql-4.8.5-13.el7.x86_64
--> Processing Dependency: libmysqlclient.so.18(libmysqlclient_18)(64bit) for package: perl-DBD-MySQL-4.023-5.el7.x86_64
--> Processing Dependency: libmysqlclient.so.18(libmysqlclient_18)(64bit) for package: 2:postfix-2.10.1-6.el7.x86_64
--> Processing Dependency: libmysqlclient.so.18(libmysqlclient_18)(64bit) for package: 1:qt-mysql-4.8.5-13.el7.x86_64
---> Package mariadb-server.x86_64 1:5.5.52-1.el7 will be obsoleted
--> Processing Dependency: mariadb-server for package: akonadi-mysql-1.9.2-4.el7.x86_64
---> Package mysql-community-libs.x86_64 0:5.7.19-1.el7 will be obsoleting
--> Running transaction check
---> Package mariadb-server.x86_64 1:5.5.52-1.el7 will be obsoleted
--> Processing Dependency: mariadb-server for package: akonadi-mysql-1.9.2-4.el7.x86_64
---> Package mysql-community-libs-compat.x86_64 0:5.7.19-1.el7 will be obsoleting
--> Finished Dependency Resolution
Error: Package: akonadi-mysql-1.9.2-4.el7.x86_64 (@anaconda)
           Requires: mariadb-server
           Removing: 1:mariadb-server-5.5.52-1.el7.x86_64 (@anaconda)
               mariadb-server = 1:5.5.52-1.el7
           Obsoleted By: mysql-community-server-5.7.19-1.el7.x86_64 (mysql57-community)
               Not found
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest

1.使用rpm 命令查找出要删除的mariadb文件,命令如下

rpm -pa | grep mariadb

可能出现结果

mariadb-libs-5.5.56-2.el7.x86_64

删除上面的程序

yum -y remove mariadb-libs.x86_64

至此，原有的mysql和mariadb数据库就删除了

1. 安装mysql官网提供的mysql repo源

启动mysqld服务，并设为开机自动启动。命令：

systemctl start mysqld.service //这是centos7的命令
systemctl enable mysqld.service

1.编辑MyQL配置文件添加以下内容

[root@localhost etc]# vim /etc/my.cnf

添加以下内容

default-authentication-plugin=mysql_native_password #配置文件本来就有去掉注释即可
symbolic-links=0
skip-grant-tables

保存后退出。

2. 重启MySQL服务

systemctl restart mysqld

3.无密码登录MySQL

mysql -u root -p

演示如下：

[root@localhost etc]# mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or g.
Your MySQL connection id is 7
Server version: 8.0.16 MySQL Community Server - GPL

Copyright (c) 2000, 2019, 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> 

Enter password：直接敲回车

4. 进入Mysql操作界面后，执行如下

（1）将原密码设置为空

update user set authentication_string=’’ where user=‘root’;

（2） 将root密码设置Haha@123，注意Mysql8密码设置规则必须是大小写字母+特殊符号+数字的类型

alter user ‘root’@‘localhost’ identified by ‘Haha@123’;

（3）将host更改% 方便远程接入

update user set host =’%’ where user=‘root’;

（4）使用已经设置的密码来更改加密方式

ALTER USER ‘root’@’%’ IDENTIFIED BY ‘Haha@123’ PASSWORD EXPIRE NEVER;

（5）使用新的加密方式重新设置密码

ALTER USER ‘root’@’%’ IDENTIFIED WITH mysql_native_password BY 'Haha@5678;

刷新

flush privileges;

重启MySQL服务

systemctl restart mysqld

分析修改密码环节

我第一次操作到4小节的（3）就重启了，发现本地登录不进去，远程也登录不进去，

后来网上搜索才知道,MySQL8.0的加密规则有所改变，要想用Navicate这样的客户端

连接的话，必须修改加密规则。但是加密规则更改又必须在设置密码的情况下修改，

所以我才改了两次密码，第一次密码是Haha@123,更改完后我就有资格修改加密规则

了，等我加密规则修改后，我就再用新的加密规则把密码再改一次，这之后刷新，然后

重启，我就可正常使用Mysql了。