There's some problem with the solution for questions 3.31 and 3.32

[roseblooming]

My answers are as follows:

    #3.31
    select ID,name
    from instructor
    where ID not in (
    	select ID
    	from teaches
    	where (course_id,sec_id,semester,year) in (
        	select course_id,sec_id,semester,year
        	from takes
        	where grade like 'A%'));

    #3.32
    select instructor.ID,name
    from (instructor natural join teaches) join takes 
    using (course_id,sec_id,semester,year)
    where grade is not null 
    and not exists (select *
                    from teaches join takes 
                    using (course_id,sec_id,semester,year)
                    where teaches.ID=instructor.ID 
                    and grade like 'A%')

[noahabe]

I will definitely look into it 🙏.