SQL многие ко многим выбирают

Question

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

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

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

Как бы я создал запрос SQL, чтобы он выбирал все имена от производителя, когда id_category равен чему-то?

Answer 1

Это простое внутреннее объединение таблиц:

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

Запрос без объединений будет выглядеть следующим образом:

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 3

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 = ?))

Answer 4

Попробуйте что-то вроде

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 5

SELECT m.name, cp.id_category
FROM manufacturer AS M INNER JOIN product AS P
    ON M.id_manufacturer = M.id_manufacturer
 INNER JOIN category_product AS CP
    ON P.id_product = CP.id_product 
WHERE cp.id_category = 'add value'