I am not quite sure of your requirements.
You want a quiz and it has an id (say QZ1) and then you want a question with an id (say Q1) and then to associate it to the quiz... but you want to make sure that this question hasnt already been used?
If that is the case you need an association table (which i would use anyway so you could resuse the questions in other quizzes - ie you have a bank of questions and pull them out for a quiz - which is how most exams work anyway). So you have a table of quizzes each with their own id and a name (or whatever you need) and a table of questions (and probably a table of answers to the questions). Then a quiz-question association table which will have two columns (usually) one for the quiz id and one for the question id. Then make the two columns a primary key (that is the two columns together make one primary key). That forces the quizid, question id combination to be unique (and also fast for you searches etc). That way a question can only appear once in a quiz but can be in in other quizzes too as the quizid question id combination will be different.
If this is a bit confusing let me know and i will try and clarify
