INNER and LEFT JOIN on mysql - mysql

Question

I have the needing to chain some joins queries, and I am not able to get the result that I want.
I have many tables to save some product info:
-Products: Name and description in many languages.
-Products_attributes: Some common attributes of the products like the provider or the buying price.
-Products_locations: Info concerning the locations that sell a certain product, like stock, or the selling price.
-Other important table is the Companies one: some of this companies could be a provider.
Well, this is my query:
SELECT p.id
, p.name nameProduct
, p.reference refProduct
, a.buy_price priceProduct
, l.active
, l.sell_price
, l.stock stockProduct
, c.title p_name
FROM products p
LEFT JOIN products_location l
ON l.product_reference = p.reference
AND l.active = 1
AND l.location_id = 4
JOIN products_attributes a
ON a.product_reference = p.reference
AND p.lang = 'es'
AND a.provider = 6
JOIN companies c
ON a.provider = c.id
AND c.id = 6
What I want to do is get all products of a certain provider, if the location from where is executing the query has this product, the row of the result must return too the concerning at this product<->location, in contrary it must return NULL in the column related to this relation.
At the moment, with this query, all what I am getting is the products of a provider where has a relation between the product<->location (through products_location table).
Any way to do that??
Thank you.
EDIT
An example about what I trying to get could be something like this:
TABLE: Companies
id | Title
1 | SomeName
6 | ProviderName
TABLE: Products
id | reference | name | lang
1 | 11111 | 1_es | es
2 | 11111 | 1_en | en
3 | 22222 | 2nam | es
4 | 33333 | 3nam | es
5 | 44444 | 4nam | es
6 | 55555 | 5nam | es
TABLE: Products_atributte
id | product_reference | buy_price | provider
1 | 11111 | 10 | 6
1 | 22222 | 15 | 6
1 | 33333 | 20 | 6
1 | 44444 | 12 | 1
1 | 55555 | 13 | 1
TABLE: Products_locations
id | product_reference | location_id | sell_price | stock | active
1 | 11111 | 4 | 26 | 10 | 1
1 | 11111 | 5 | 25 | 13 | 1
1 | 22222 | 5 | 20 | 13 | 1
1 | 44444 | 5 | 21 | 1 | 1
1 | 55555 | 5 | 22 | 2 | 1
AND THE RESULT MUST BE SOMETHING LIKE THIS:
nameProduct | refProduct | priceProduct | active | sell_price | stockProduct | p_name
1_es | 11111 | 10 | 1 | 26 | 10 | ProviderName
2nam | 22222 | 15 | NULL | NULL | NULL | ProviderName
3nam | 33333 | 20 | NULL | NULL | NULL | ProviderName
If I use a LEFT JOIN only in the products_locations table, I don´t get the two last rows, and if I use LEFT JOIN with all the tables I get duplicates product references, also I get products provided by other providers (in the example 1-> SomeName).

Answer 1

You were correct to LEFT JOIN the products and products_location tables. However, you used INNER JOIN for the other two tables in the query and I believe that this may be the reason why you are only seeing records which have a relation between product and location. The logic would be that a product which does not have a location also does not have an entry in, for example, the products_attributes table. Hence, the non matching records you want to retain would be filtered off downstream by an INNER JOIN. To remedy this, use LEFT JOIN everywhere:
SELECT products.id,
products.name AS nameProduct,
products.reference AS refProduct,
products_attributesbuy_price AS priceProduct,
products_location.active,
products_location.sell_price,
products_location.stock AS stockProduct,
provider.title AS p_name
FROM products
LEFT JOIN products_location
ON products_location.product_reference = products.reference AND
products_location.active = 1 AND
products_location.location_id = 4
LEFT JOIN products_attributes
ON products_attributes.product_reference = products.reference AND
products.lang = 'es' AND
products_attributes.provider = 6
LEFT JOIN companies AS provider
ON products_attributes.provider = provider.id AND
provider.id = 6