Are you wanting to read SQL queries people write or are you wanting to read the source code to MySQL. I could interpret this either way. SQL isn't hard to pic

Are you wanting to read SQL queries people write or are you wanting to read the source code to MySQL. I could interpret this either way. SQL isn't hard to pick up. Do a few online tutorials, setup an install and start experimenting. You can find online datasets even that you can load and query which will force you to use SQL which will reenforce the tutorials. If you mean MySQL source that powers MySQL then that is a much bigger hill to climb. You'd be smart to start with smaller, more simplistic code bases at first and work your way up.