How many repair assignments are there in file?
select count(*) from repair_assignment
Show me their names.
select technician_id from repair_assignment
What about the technicians in file who are not one of those?
select technician_id from technician where technician_id not in (select technician_id from repair_assignment)
Show me their names.
select name from technician where technician_id not in (select technician_id from repair_assignment)