Show me first names for employees serving 20 customers.
select t1.firstname from customer as t1 join employee as t2 on t1.supportrepid = t2.employeeid group by t1.supportrepid having count(*) = 20
Show me their last names.
select t1.lastname from customer as t1 join employee as t2 on t1.supportrepid = t2.employeeid group by t1.supportrepid having count(*) = 20
Show me the same for employees serving no more than 20 customers.
select t1.lastname from customer as t1 join employee as t2 on t1.supportrepid = t2.employeeid group by t1.supportrepid having count(*) <= 20