instruction: For those employees who was hired before 2002-06-21, find job_id and the sum of employee_id , and group by attribute job_id, and visualize them by a bar chart, rank from low to high by the Y-axis.
response: SELECT JOB_ID, SUM(EMPLOYEE_ID) FROM employees WHERE HIRE_DATE < '2002-06-21' GROUP BY JOB_ID ORDER BY SUM(EMPLOYEE_ID)