Show the first names and ids of employees serving 10 customers.
select t1.firstname, t1.supportrepid from customer as t1 join employee as t2 on t1.supportrepid = t2.employeeid group by t1.supportrepid having count(*) = 10
Show me those serving at least 10 customers.
select t1.firstname, t1.supportrepid from customer as t1 join employee as t2 on t1.supportrepid = t2.employeeid group by t1.supportrepid having count(*) >= 10