What is the difference between SQL and MySQL? 

I can't remember if we covered this at the beginning of the course, but why would we choose a relational database (MySQL) to a non relational database (or vice versa)?

Do we use MySQL as a backend database similar to what we are doing with MongoDB right now?

How do modern relational databases optimize joins when handling large datasets, and what are the implications of these optimizations for database design and query performance?

Can we talk about different types of joins (inner, left, right, etc.)?

I might have missed this in the reading, but why does using the source command to run the file result in "database changed" being printed out while the second way to run a file does not result in the database being changed?