Table schema:
CREATE TABLE CUSTOMER (FirstName VARCHAR, SupportRepId VARCHAR); CREATE TABLE EMPLOYEE (EmployeeId VARCHAR)

Question: Please show the employee first names and ids of employees who serve at least 10 customers.
SQL: 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