Who are the employees that actually support customers?
select t1.first_name, t2.last_name from employees as t1 join customers as t2 on t1.id = t2.support_rep_id
How about the most?
select count(*) from employees as t1 join customers as t2 on t1.id = t2.support_rep_id group by t1.id order by count(*) desc limit 1
What is the name of the employee that supports this many!
select t1.first_name, t1.last_name from employees as t1 join customers as t2 on t1.id = t2.support_rep_id group by t1.id order by count(*) desc limit 1