Which students have taken Biology courses?
select * from takes as t1 join course as t2 on t1.course_id = t2.course_id where t2.dept_name = 'Biology'
What are the names of all students who did not take that class?
select name from student where id not in (select t1.id from takes as t1 join course as t2 on t1.course_id = t2.course_id where t2.dept_name = 'Biology')