1.配置
系統：centos7.6
mysql版本：mysql 5.7
2.這里原先的方案為：直接卸載mysql
3.遇到的問題：
安裝mysql的最后一步時
#yum install mysql-community-server
遇到以下錯誤：
Error: Package: 2:postfix-2.10.1-7.el7.x86_64 (@anaconda)
Requires: libmysqlclient.so.18(libmysqlclient_18)(64bit)
Removing: 1:mariadb-libs-5.5.60-1.el7_5.x86_64 (@anaconda)
libmysqlclient.so.18(libmysqlclient_18)(64bit)
Obsoleted By: mysql-community-libs-5.7.29-1.el6.x86_64 (mysql57-community-dmr)
Not found
Updated By: 1:mariadb-libs-5.5.64-1.el7.x86_64 (base)
libmysqlclient.so.18(libmysqlclient_18)(64bit)
Error: Package: 2:postfix-2.10.1-7.el7.x86_64 (@anaconda)
Requires: libmysqlclient.so.18()(64bit)
Removing: 1:mariadb-libs-5.5.60-1.el7_5.x86_64 (@anaconda)
libmysqlclient.so.18()(64bit)
Obsoleted By: mysql-community-libs-5.7.29-1.el6.x86_64 (mysql57-community-dmr)
~libmysqlclient.so.20()(64bit)
Updated By: 1:mariadb-libs-5.5.64-1.el7.x86_64 (base)
libmysqlclient.so.18()(64bit)
Error: Package: mysql-community-server-5.7.29-1.el6.x86_64 (mysql57-community-dmr)
Requires: libsasl2.so.2()(64bit)
You could try using --skip-broken to work around the problem
You could try running: rpm -Va --nofiles --nodigest
查詢各種信息；基本確定是因為 mysql 的依賴問題。剛開始，最快的解決方案就是卸載重裝.
4.解決方法：
卸載，重裝了兩遍還是出現同樣的錯誤。
提示：
Error: Package: mysql-community-server-5.7.29-1.el6.x86_64 (mysql57-community-dmr)
Requires: libsasl2.so.2()(64bit)
You could try using --skip-broken to work around the problem
You could try running: rpm -Va --nofiles --nodigest
最后解決方案：
修改vim /etc/yum.repos.d/mysql-community.repo 源文件
這里注意，禁用mysql其他版本，只啟用5.7
更改2點，保存后重新安裝
enabled=0
gpgcheck=0
yum install mysql-community-server
以上操作完成后，完美解決
下面來說說如何卸載
4.1.快速刪除
yum remove mysql mysql-server mysql-libs mysql-server
4.2.查找殘留文件
rpm -qa | grep -i mysql
4.3將查詢出來的文件逐個刪除，如：
yum remove mysql-community-common-5.7.29-1.el6.x86_64
4.4.查找殘留目錄
whereis mysql
4.5逐條刪除目錄，如：
rm –rf /usr/lib64/mysql
####這些操作完成后更新源
5.給CentOS添加rpm源，並且選擇較新的源
wget dev.mysql.com/get/mysql-community-release-el6-5.noarch.rpm --no-check-certificate
yum localinstall mysql-community-release-el6-5.noarch.rpm
yum repolist all | grep mysql
yum-config-manager --disable mysql55-community
yum-config-manager --disable mysql56-community
yum-config-manager --enable mysql57-community-dmr
yum repolist enabled | grep mysql
6.查詢mysql所用的版本：
yum repolist all | grep mysql
7.檢測系統是否存在mysql
yum list installed|grep mysql
8.刪除mysql依賴項
yum-yremovemysql-libs.x86_64
9.備注：需要掌握的yum命令
9.1安裝yum 倉庫列表：
yum -y localinstall mysql57-community-release-el6-8.noarch.rpm
9.2查看：
yum list | grep mysql
9.3安裝mysql
yum -y install mysql-community-server
10.如何禁用或啟用mysql的其他版本：
方法1:
官網文檔上給出的執行命令
yum-config-manager --disable mysql56-community
yum-config-manager --enable mysql57-community
方法2：修改配置文件
vi /etc/yum.repos.d/mysql-community.repo
修改完成后再次查看：yum repolist all | grep mysql
