MariaDB is in most aspects identical to MySQL.

Differences between MySQL and MariaDB can be found at:
http://askmonty.org/wiki/index.php/MariaDB_versus_MySQL

The MariaDB references manual can be found at:
http://askmonty.org/wiki/index.php/Manual

The MySQL Reference Manual is available in various formats on
http://dev.mysql.com/doc; if you're interested in the DocBook XML
sources go to http://svn.mysql.com.