SQL多對多選擇

Question

category_product 
--------------- 
id_category 
id_product 

product 
--------------- 
id_product 
id_manufacturer 

manufacturer 
--------------- 
id_manufacturer 
name 

如何創建SQL查詢，以便在id_category等於某個值時從製造商選擇所有名稱？

Answer 1

這是一個簡單的內部連接的表：

SELECT m.name, cp.id_category 
FROM manufacturer as m 
INNER JOIN product as p 
    ON m.id_manufacturer = p.id_manufacturer 
INNER JOIN category_product as cp 
    ON p.id_product = cp.id_product 
WHERE cp.id_category = 'some value' 

Answer 2

嘗試像

SELECT m.* 
FROM  category_product cp INNER JOIN 
      product p ON cp.id_product = p.id_product INNER JOIN 
      manufacturer m ON p.id_manufacturer = m.id_manufacturer 
WHERE  cp.id_category = <your_value> 

Answer 3

查詢，而不加入將類似於以下內容：

SELECT m.name 
FROM manufacturer as m, product as p, category_product as cp 
WHERE cp.id_category = <your value> 
     AND cp.id_product = p.id_product 
     AND p.id_manufacturer = m.id_manufacturer 

Answer 4

Select M.name 
From manufacturer M 
Where M.id_manufacturer in (Select P.id_manufacturer 
           From product P 
           Where P.id_product in (Select C.id_product 
                 From category_product C 
                 Where C.id_category = ?))