Join in Query WHERE clause

Question

I have several tables I"m trying to get data out of efficiently.

I have a drafted query as such:

SELECT products.id, products.name products.extended_description, products.catalogid, products.image1, products.image2, products.stock, products.price, manufacturer.manufacturer, products.weight
FROM products 
JOIN manufacturer ON (products.manufacturer = manufacturer.id)
WHERE category.category_name = ?;

Obviously this is a broken query, but I'm not sure how to fix this. I need to somehow join category table to product_category table which is related to products table via the products.catalogid field.

My feeble attempt is as such:

SELECT products.id, products.name products.extended_description, products.catalogid, products.image1, products.image2, products.stock, products.price, manufacturer.manufacturer, products.weight
FROM products
JOIN manufacturer ON (products.manufacturer = manufacturer.id)
FROM category
JOIN product_category ON (category.id = (SELECT product_category.id FROM product_category WHERE product_category.catalogid /*I'm so lost...*/))
WHERE category.category_name = ?;

Basically I need to query the db for all the info in the SELECT clause where the category name is "NEW"... and I'm completely stumped (my SQL obviously needs some work!)

Answer 1

Something like this, just keeping joining and joining and....

SELECT
    *
FROM
    products as p
JOIN
    manufacturer as m
ON
    p.manufacturer = m.id
JOIN
    product_category as pc
ON
    pc.product = p.id
JOIN
    category as c
ON
    c.id=pc.category
WHERE
    c.name = "NEW"

Answer 2

Since you've got a product_category table, it appears that your product may belong to multiple categories. In cases like that, you want to check if a category that you are looking for is among the categories assigned to your product.

One way of doing it is with an EXISTS condition:

SELECT p.id, p.name p.extended_description, p.catalogid, p.image1, p.image2, p.stock, p.price, m.manufacturer, p.weight
FROM products p
JOIN manufacturer m ON (p.manufacturer = m.id)
WHERE
EXISTS (
    SELECT *
    FROM product_category pc
    JOIN category c ON c.id=pc.categoryId
    WHERE pc.productId = p.id
    AND c.category.category_name = ?
)

I assumed that the product_category many-to-many table has columns categoryId and productId which bring together the IDs of the product and a category to which that product belongs.