SELECT id FROM teaches WHERE semester  =  'Fall' AND YEAR  =  2009 EXCEPT SELECT id FROM teaches WHERE semester  =  'Spring' AND YEAR  =  2010
Find the id of instructors who taught a class in Fall 2009 but not in Spring 2010.
SELECT id FROM teaches WHERE semester = 'Fall ' AND YEAR = 2009 EXCEPT SELECT id FROM teaches WHERE semester = 'Spring ' AND YEAR = 2010
select id from teaches where semester = value and year = value except select id from teaches where semester = value and year = value
Find the id of instructors who taught a class in Fall 2009 but not in Spring 2010 .