加入兩個一對多表

Question

我有這兩個表，我必須寫這個SQL查詢（Microsoft Access中）之間：

• 撰寫出了每個作者的銷量任何書籍有多少頭銜查詢（book_id）和多少個單位（訂購的數量），他們賣

我試圖與該查詢，但它不工作

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; 

，但它不工作，因爲它計算同一本書多次從customersOrders

Answer 1

這個怎麼樣了？

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;