How to Uninstall MariaDB from Linux CentOS
To uninstall MariaDB from Linux CentOS you can use below command
# sudo yum remove MariaDB-server MariaDB-client
If you don’t have MariaDB-client installed on the Linux then you can simply use above command without MariaDB-client.
The uninstallation does not remove the data directory /var/lib/mysql. If you need to use then you can leave the directory for future use, otherwise you can delete by using below command
# sudo rm -r /var/lib/mysql
How to Uninstall MariaDB from Linux CentOS
You still have the MariaDB yum repository on your system. As long as you do so, MariaDB will continue to replace MySQL.
To resolve the issue, remove the MariaDB repository. Do this by locating the file (it may be named something like mariadb.repo) in the /etc/yum.repos.d directory. Once you locate the file, you may remove it, or you may edit the file and change enabled=1 to enabled=0.
How to Uninstall MariaDB from Linux CentOS
If you must have mysql you need to add the mysql-community repo sudo rpm -Uvh http://dev.mysql.com/get/mysql-community-release-el7-5.noarch.rpm and then you can install MySQLl like you normally do.
On Ubuntu you need remove dbconfig-mysql and install dbconfig-no-thanks
Source: https://serverfault.com/