How many people are in the staff?
select count ( * ) from staff
How many of these people cancelled their lesson?
select count ( distinct t2.staff_id ) from lessons as t1 join staff as t2 on t1.staff_id = t2.staff_id where t1.lesson_status_code = "Cancelled"
What is the first name of these people?
select t2.first_name from lessons as t1 join staff as t2 on t1.staff_id = t2.staff_id where t1.lesson_status_code = "Cancelled" group by t2.first_name