Find the name of the department which has the highest average salary of professors
select dept_name from instructor group by dept_name order by avg ( salary ) desc limit 1
what is the average salary of a physics professor?
select avg ( salary ) from instructor where dept_name = 'Physics'
find the department name which has the lowest average salary of professors
select dept_name from instructor group by dept_name order by avg ( salary ) asc limit 1