If you can an error like “com.mysql.jdbc.driver not found” when trying to connect to a MySQL database in Libreoffice Base you probably need to do the following:
# emerge -avq dev-java/jdbc-mysql
Check the location of the jdbc-mysql archive:
# ls /usr/share/jdbc-mysql/lib/jdbc-mysql.jar
If it is not found:
# locate jdbc-mysql
There will probably be only one .jar in the results.
Add that file path to Class Path in Libreoffice Base (Tools, Options, Java, Class Path).