title: how to enforce constraint in sql?
body: <p>I have a question regarding enforce a constraint to my table.
  I have a table called workson and a table called staff, each staff has specific title(supervisor,authorizer,manager,...). I need to ensure that the supervisor and the authorizer cannot be the same staff on workson table.The cardinality between them is many to many. I am not sure how to do it.
  Can you please advise me to solve this problem?</p>
  
  <p>Thanks</p>