一、卸载MySql
卸载之前关闭所有mysql服务
systemctl stop mysqld
查看进程,还存在的话，直接kill掉
ps -ef | grep mysql
1.首先查看已安装的mysql
rpm -qa | grep -i mysql
[root@iZwz9dev0583p7pppda7ymZ ~]# rpm -qa | grep -i mysql
mysql-community-common-5.7.35-1.el7.x86_64
mysql-community-server-5.7.35-1.el7.x86_64
mysql-community-client-5.7.35-1.el7.x86_64
mysql80-community-release-el7-3.noarch
mysql-community-libs-5.7.35-1.el7.x86_64
2.逐个卸载掉
rpm -e mysql-community-common-5.7.35-1.el7.x86_64
rpm -e mysql-community-server-5.7.35-1.el7.x86_64
rpm -e mysql-community-client-5.7.35-1.el7.x86_64
rpm -e mysql-community-libs-5.7.35-1.el7.x86_64
mysql80-community-release-el7-3.noarch这是yum库的rpm包，如果版本符合，可以不卸载
注意：官网的mysql80-community-release-el8-1.noarch内只包含了mysql8.0以上版本，如果需要安装mysql5.7，需要使用mysql80-community-release-el7-3.noarch，el7表示操作系统版本linux7。
3. 卸载其他相关文件
1⃣️查找出来后使用rm -rf命令逐个删除
find / -name mysql
2⃣️或者直接使用如下命令删除
find / -name mysql -exec rm -rf {} \;
二、安装MySql
1.安装mysql的rpm源
centOS8中的yum库默认的是mariaDB，我们需要下载mysql80-community-release-el7-3.noarch，里面包含了5.6，5.7，8.0等版本。官网
wget http://dev.mysql.com/get/mysql80-community-release-el7-3.noarch.rpm
安装mysql的rmp
rpm -ivh mysql80-community-release-el7-3.noarch.rpm
查看将要安装的mysql相关文件
yum repolist all | grep mysql
[root@iZwz9dev0583p7pppda7ymZ ~]# yum repolist all | grep mysql
Repository epel is listed more than once in the configuration
mysql-cluster-7.5-community MySQL Cluster 7.5 Community 禁用
mysql-cluster-7.5-community-source MySQL Cluster 7.5 Community - Source 禁用
mysql-cluster-7.6-community MySQL Cluster 7.6 Community 禁用
mysql-cluster-7.6-community-source MySQL Cluster 7.6 Community - Source 禁用
mysql-cluster-8.0-community MySQL Cluster 8.0 Community 禁用
mysql-cluster-8.0-community-source MySQL Cluster 8.0 Community - Source 禁用
mysql-connectors-community MySQL Connectors Community 启用
mysql-connectors-community-source MySQL Connectors Community - Source 禁用
mysql-tools-community MySQL Tools Community 启用
mysql-tools-community-source MySQL Tools Community - Source 禁用
mysql-tools-preview MySQL Tools Preview 禁用
mysql-tools-preview-source MySQL Tools Preview - Source 禁用
mysql55-community MySQL 5.5 Community Server 禁用
mysql55-community-source MySQL 5.5 Community Server - Source 禁用
mysql56-community MySQL 5.6 Community Server 禁用
mysql56-community-source MySQL 5.6 Community Server - Source 禁用
mysql57-community MySQL 5.7 Community Server 启用
mysql57-community-source MySQL 5.7 Community Server - Source 禁用
mysql80-community MySQL 8.0 Community Server 禁用
mysql80-community-source MySQL 8.0 Community Server - Source 禁用
默认情况下mysql80-community是启用的，mysql57-community是禁用的，用以下命令改变将要安装的版本
yum-config-manager --disable mysql80-community
yum-config-manager --enable mysql57-community
如果出现yum-config-manager: command not found,安装yum的utils工具即可
yum -y install yum-utils
安装完再执行上一步
2.安装MySql
yum -y install mysql-community-server
如果遇到Error: Unable to find a match: mysql-community-server
先执行以下命令，关闭当前的MariaDB，再执行上面的安装命令
yum module disable mysql
安装完毕，查看MySql版本
[root@iZwz9dev0583p7pppda7ymZ ~]# mysql --version
mysql Ver 14.14 Distrib 5.7.35, for Linux (x86_64) using EditLine wrapper
启动MySql
systemctl start mysqld
查看MySql状态
[root@iZwz9dev0583p7pppda7ymZ ~]# systemctl status mysqld
● mysqld.service - MySQL Server
Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
Active: active (running) since Sat 2021-07-31 16:51:39 CST; 5h 57min ago
Docs: man:mysqld(8)
http://dev.mysql.com/doc/refman/en/using-systemd.html
Process: 1585 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS)
Process: 1563 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
Main PID: 1587 (mysqld)
Tasks: 30 (limit: 23683)
Memory: 228.7M
CGroup: /system.slice/mysqld.service
└─1587 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid
7月 31 16:51:37 iZwz9dev0583p7pppda7ymZ systemd[1]: mysqld.service: Succeeded.
7月 31 16:51:37 iZwz9dev0583p7pppda7ymZ systemd[1]: Stopped MySQL Server.
7月 31 16:51:37 iZwz9dev0583p7pppda7ymZ systemd[1]: Starting MySQL Server...
7月 31 16:51:39 iZwz9dev0583p7pppda7ymZ systemd[1]: Started MySQL Server.
接下来是进入数据库，先查看数据库root用户的初始密码
grep "password" /var/log/mysqld.log
最后面冒号后的就是DNDcewvug3.-
[root@iZwz9dev0583p7pppda7ymZ ~]# grep "password" /var/log/mysqld.log
2021-07-31T08:26:01.664775Z 1 [Note] A temporary password is generated for root@localhost: DNDcewvug3.-
如果提示没有/var/log/mysqld.log或者sock之类的文件，重启服务器即可
通过以下命令进入数据库
mysql -uroot -p
更改root用户密码（不改的话无法进行其他操作）
ALTER USER USER() IDENTIFIED BY 'root';
密码设置太简单有可能出现ERROR 1819 (HY000): Your password does not satisfy the current policy requirements
查看密码规则
SHOW VARIABLES LIKE 'validate_password%';
mysql> SHOW VARIABLES LIKE 'validate_password%';
+--------------------------------------+-------+
| Variable_name | Value |
+--------------------------------------+-------+
| validate_password_check_user_name | OFF |
| validate_password_dictionary_file | |
| validate_password_length | 6 |#默认情况下这里是8
| validate_password_mixed_case_count | 1 |
| validate_password_number_count | 1 |
| validate_password_policy | LOW |#默认情况下这里是MEDIUM
| validate_password_special_char_count | 1 |
+--------------------------------------+-------+
7 rows in set (0.00 sec)
如果想要设置简单密码，可以更改规则中的长度和验证策略
set global validate_password_length=4;
set global validate_password_policy=0;
密码规则如下图
image.png
最后，就可以创建数据库了
create database testDB
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