在两个一对多表之间加入

Question

我有这两个表，我必须编写这个SQL查询（Microsoft Access）：

• 为每个出售任何图书的作者撰写一个查询，显示他们销售了多少图书（book_id）和多少单位（订购数量）

我已尝试使用此查询，但它无法正常工作

SELECT authors.author_id, Count(orders.book_id) AS CountOfbook_id,
Sum(orders.quantity_ordered) AS SumOfquantity_ordered
FROM authors 
LEFT JOIN orders ON authors.book_id = orders.book_id
GROUP BY authors.author_id;

但它不起作用，因为它重复了同一本书从customersOrders

获得的许多次

Answer 1

这个怎么样？

select author,sum(CountOfbook_id), sum(SumOfquantity_ordered)
from (
    SELECT authors.author_id as author, Count(orders.book_id) AS CountOfbook_id,
    Sum(orders.quantity_ordered) AS SumOfquantity_ordered
    FROM authors 
    LEFT JOIN orders ON authors.book_id = orders.book_id
    GROUP BY authors.author_id,authors.book_id;)
group by author;