Please show the employee first names and ids of employees who serve 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
employees who serve at least 10 customers refers to COUNT(*) >= 10; employee first names refer to T2.FirstName; employee ids refer to T1.SupportRepId;