Huang Chung-Yu,
Welcome to JavaRanch!
I'm not sure I understand your question. Are you looking for a way to get a list of the names of people (or a single person) who got the highest grade, so that you can display it in a Swing application?
If so, such a query might look like this:
It's a bit simpler if you have students and grades in the same table.
As for the JLabel, you're on your own!
Jules