Someone will probably tell me that this is an elementary-level
topic, but I got some good questions regarding joins from my most
recent ZCE class students, so I thought I'd put down the examples
that I used to explain this to them. Being able to join with
confidence is a key skill, because it means that you can refactor
and normalise your data, without worrying about how hard
something will be to retrieve.
The database structure I'm using here looks like this (the same example that I used when I wrote the Databases chapter for PHP Master):