Here are some links to external MariaDB, MySQL and SQL tutorials that may be of interest

MariaDB-Focused Tutorials

• Tutorialspoint MariaDB tutorial for beginners
• MariaDB Tutorial by "Tech on the net"
• Learn MySQL / MariaDB for Beginners
• MariaDB Tutorial from javatpoint

MySQL-Focused Tutorials (But Should Work For MariaDB Too)

• mysqltutorial. Site with a lot of MySQL usage information and also how to connect to MySQL from different programming languages.
• MySQL Tutorial for Beginners Learn in 7 Days
• MySQL Tutorial from javatpoint
• MySQL Tutorial from w3resource
• MySQL by Examples for Beginners
• MySQL Tutorial – A Beginner’s Guide To Learn MySQL
• Php/MySQL Tutorial from tizag
• PHP & MySQL Tutorial from siteground

General SQL Tutorials

• w3schools general SQL tutorial
• sqltutorial. Helps you get started with SQL quickly and effectively through many practical examples.

See Also

• MariaDB Knowledge Base Training and Tutorials