Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE EMPLOYEE (EmployeeId VARCHAR)
TABLE: CREATE TABLE CUSTOMER (LastName VARCHAR, SupportRepId VARCHAR)

### Question ###
Please show the employee last names that serves no more than 20 customers.

### Accurate SQL ###

SELECT T1.LastName FROM CUSTOMER AS T1 JOIN EMPLOYEE AS T2 ON T1.SupportRepId = T2.EmployeeId GROUP BY T1.SupportRepId HAVING COUNT(*) <= 20