What are the ids of courses offered in Fall of 2009 but not in Spring of 2010?
SELECT course_id FROM SECTION WHERE semester  =  'Fall' AND YEAR  =  2009 EXCEPT SELECT course_id FROM SECTION WHERE semester  =  'Spring' AND YEAR  =  2010
courses offered in Fall of 2009 refers to semester = 'Fall' AND year = 2009; courses not offered in Spring of 2010 refers to EXCEPT SELECT course_id FROM SECTION WHERE semester = 'Spring' AND year = 2010;