쿼리 #8.sql

-- amount는 판매금액, 직원별 평균 판매금액 알고 싶다.
SELECT * FROM payment;

SELECT	p.staff_id, 
			s.first_name, 
			s.last_name, 
			AVG(p.amount) AS avg_amount 
FROM payment p
inner JOIN staff s
ON p.staff_id = s.staff_id
GROUP BY p.staff_id;

SELECT * FROM staff;