It happens. Sometimes we mess up our demo database. Sometimes the installation option is missed and it doesn’t get installed. You don’t need to re-install all of MySQL to get the demo database. They can be installed using scripts.
You can download the Sakila database scripts here: https://downloads.mysql.com/docs/sakila-db.zip
Once downloaded, you can follow the steps on MySQL’s guide to run them: MySQL :: Sakila Sample Database :: 4 Installation
To execute the file (be sure you are in the same directory as the scripts) you can run:
source the-script-name.sql