About MySQL
The database under most of the web you run.
MySQL is the widely deployed open-source relational database now owned by Oracle. It powers WordPress, Magento and most LAMP stacks, and stays a default choice for transactional workloads in ecommerce, SaaS and internal tools. If a PHP or Node backend was built in the last fifteen years, there is a good chance the operational data lives in MySQL.
The point of pulling MySQL into a warehouse is that most MySQL databases carry years of history that the business never looks at properly. Reports run directly on the live database are slow, fragile and compete with end-user traffic, and the weekly dump someone set up long ago is already a bad starting point. In a warehouse, MySQL joins CRM, accounting and commerce data without putting reporting load on the system that has to stay up.