Which engineer has visited the least number of times? Show the id, first and last names of that engineer.
select t1.engineer_id, t1.first_name, t1.last_name from maintenance_engineers as t1 join engineer_visits as t2 group by t1.engineer_id order by count(*) asc limit 1
Do the same for the engineer who has visited the most times.
select t1.engineer_id, t1.first_name, t1.last_name from maintenance_engineers as t1 join engineer_visits as t2 group by t1.engineer_id order by count(*) desc limit 1