How to create unique random integer?

is there any posible way to create unique random integer. I know how to make Array or List with unique numbers, but fact is that I need each time different number cause I am creating something like exam, and I am taking values with different id-s from db . If I take duplicate number I would make two same questions on exam.

If there is no way to do it, what do you suggest? how to handle problem. I need to generate different id each time from db. Thanks in advance.