-- Database schema
| classroom : building [ TEXT ] primary_key , room_number [ TEXT ] , capacity [ INT ] | department : dept_name [ TEXT ] primary_key , building [ TEXT ] , budget [ INT ] | course : course_id [ TEXT ] primary_key , title [ TEXT ] , dept_name [ TEXT ] course.dept_name = department.dept_name , credits [ INT ] | instructor : ID [ TEXT ] primary_key , name [ TEXT ] , dept_name [ TEXT ] instructor.dept_name = department.dept_name , salary [ INT ] | section : course_id [ TEXT ] primary_key section.course_id = course.course_id , sec_id [ TEXT ] , semester [ TEXT ] , year [ INT ] , building [ TEXT ] section.building = classroom.building , room_number [ TEXT ] section.room_number = classroom.room_number , time_slot_id [ TEXT ] | teaches : ID [ TEXT ] primary_key teaches.ID = instructor.ID , course_id [ TEXT ] teaches.course_id = section.course_id , sec_id [ TEXT ] teaches.sec_id = section.sec_id , semester [ TEXT ] teaches.semester = section.semester , year [ INT ] teaches.year = section.year | student : ID [ TEXT ] primary_key , name [ TEXT ] , dept_name [ TEXT ] student.dept_name = department.dept_name , tot_cred [ INT ] | takes : ID [ TEXT ] primary_key takes.ID = student.ID , course_id [ TEXT ] takes.course_id = section.course_id , sec_id [ TEXT ] takes.sec_id = section.sec_id , semester [ TEXT ] takes.semester = section.semester , year [ INT ] takes.year = section.year , grade [ TEXT ] | advisor : s_ID [ TEXT ] primary_key advisor.s_ID = student.ID , i_ID [ TEXT ] advisor.i_ID = instructor.ID | time_slot : time_slot_id [ TEXT ] primary_key , day [ TEXT ] , start_hr [ INT ] , start_min [ INT ] , end_hr [ INT ] , end_min [ INT ] | prereq : course_id [ TEXT ] primary_key prereq.course_id = course.course_id , prereq_id [ TEXT ] prereq.prereq_id = course.course_id |
-- -- 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;