When I first looked at Jacob's solution, I thought "what a nice solution". Unfortunately, it is simple, understandable and easily maintainable, but it works only in an ideal life where you will never experience drop in salary to your previous level. In fact, it does not record every CHANGE, it just finds first occurence of every value... which is not always the same thing.

So, depending on what you need, you can either do with this, or look for a better solution that will show you every change in salary, no matter whether it is raise or the opposite. That would probably require a self-join, where you join each row of the table to the "previous" row and compare salary. This would be a lot easier with DATETIME column for the date instead on two columns, Year and Month.