If you want to use MySQL with MariaDB install it with
pamac install mariadb
Then run
sudo mariadb-install-db --user=mysql --basedir=/usr --datadir=/var/lib/mysql
systemctl start mariadb
and set up mariadb
sudo mariadb-secure-installation
answer the questions to set up the mariadb root user with a password.
After that you can log in without the need of sudo.
mysql -u root -p