I'm a new comer to UML. But I am well experienced in drawing db tables as well as their associations.
Can One just "extend" these tables with the addition of Techniques() below and refer to it as a UML Class Diagram?
StudentID : int
StudentNumber : string
FirstName : string
Surname : string
Making an item for each table is not a sensible practice. Its not all table must be an item inside your UML... However again... I believe this really is more for StackOverflow...
You appear to achieve the fundamentals of UML. The primary variations are that relationship types aren't the same as SQL which Java (or whatever language) data types don't match SQL data types directly, so you will need to convert individuals as you've above.
[opinion] Unless of course you've got a UML->code->UML tool I wouldn't get too hung on drawing the UML. It's mainly something for whitened boarding (IMHO) and having faith in individuals diagrams has a tendency to hurt you over time when maintenance changes make that kind of documentation obsolete. I favor to utilize a code->UML tool when searching at legacy code instead of outdated UML diagrams from design time. [/opinion]
 Since you have working code you might want to try Amateras UML in Eclipse. You are able to drag a lot of classes onto a clear document and it'll produce the UML diagram for you personally. [/edit]