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The qz_ques_catalog table is contains all questions. Each unique questionid has a Questionid is the primary key, with question name, question type and owner, and kerberos_name as required fields. All relationships to answers and feedback are associated with the this primary key, quesionid.
The association of quizzes with questions occurs in qz_section_questions. The unique secid (from qz_section) is matched with a question key (qcid) - the two foreign keys are the primary key with additional information for the order/sequence of appearance.