SELECT id FROM teaches WHERE semester  =  'Fall' AND YEAR  =  2009 EXCEPT SELECT id FROM teaches WHERE semester  =  'Spring' AND YEAR  =  2010
What are the ids of instructors who taught in the Fall of 2009 but not in the Spring of 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
What are the ids of instructors who taught in the Fall of 2009 but not in the Spring of 2010 ?