I can't import java.sql classes even that I have added them to the library

Could you please provide a project example?

Since this Java 9+ project, You need to add "requires java.sql" in your module-info.java

Easiest way to do that is press alt-enter on the import (red) and it should you the menu to do this. 

@Krishnan Thanks it solved the problem

@... Thank you very. Bless you, I was about to give up on a tutorial.