Instalación de MariaDB 10.4 en Ubuntu 18.04 LTS «bionic»

Here are the commands to run to install MariaDB 10.4 from the MariaDB repository on your Ubuntu system:

sudo apt-get install software-properties-common
sudo apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com:80 0xF1656F24C74CD1D8
sudo add-apt-repository 'deb http://ftp.hosteurope.de/mirror/mariadb.org/repo/10.4/ubuntu bionic main'

Once the key is imported and the repository added you can install MariaDB 10.4 from the MariaDB repository with:

sudo apt update
sudo apt install mariadb-server

More info:

Setting up MariaDB Repositories