Learning the foundations of any profession will help you better understand your job and in turn further your career—and database administration is no exception. Database professionals who write a lot of T-SQL code should explore T-SQL’s foundations. SQL Server’s T-SQL is based on standard SQL, which is based on the relational model, which in turn is based on mathematical foundations (i.e., set theory and predicate logic). In this article I discuss a fundamental topic in set theo...