Inflearn Community Q&A

정답 예시에서는 91개가 조회되는데 제가 생각한 쿼리는 89개만 조회가 됩니다. 쿼리가 잘못된걸 까요?

SELECT 
c.customerId `고객아이디`, 
c.customername as `고객이름`, 
sum(Quantity) as `주문량` 
FROM OrderDetails od
join Orders o on o.OrderId = od.OrderId
join Customers c on c.customerId = o.customerId
group by o.customerId
order by sum(Quantity) desc
;