Mysql Join Won't Select - php

Question

I have been doing a lots of research online and from my understanding i think my query is ok
That is why i need your help to point me out what im doing wrong.
What My Query Should Do
My query should fetch our stock level from both warehouse
Problem Is
if the product is not in both warehouse the query dont give any result.
Ok so first i have two database of warehouse stock level. that look like that.
Databases
-warehouse1
-warehouse2
Table
-product
Columns
-id
-SKU
-qty
So my Query is
SELECT
warehouse1.product.id as 1_id,
warehouse2.product.id as 2_id ,
warehouse1.product.SKU,
warehouse1.product.qty as 1_qty,
warehouse2.product.qty as 2_qty
FROM `warehouse1`.`product`
LEFT JOIN `warehouse2`.`product`
ON
(`warehouse1`.`product`.`SKU` = `warehouse2`.`product`.`SKU`)
WHERE
warehouse1.product.SKU = '$sku'
OR
warehouse2.product.SKU = '$sku'
ORDER BY
(1_qty + 2_qty) DESC
if i make the where clause like this
WHERE warehouse1.product.SKU = '$sku'
it is then working but i can't get stock from both warehouse.
What should i do if i want to receive the stock level from both warehouse even if there is no product that im asking for in this database.
Thanks

Answer 1

Try a FULL OUTER JOIN. You're using a LEFT JOIN. That requires that the DB fetch all records that match your WHERE clause on the LEFT side of the join, which is warehouse1, and any potentially matching records from warehouse2 (the right side of the join). If a SKU exists only in warehouse2, you don't see it.
Switching to a FULL OUTER JOIN forces the DB to fetch all matching records from BOTH sides of the join, regardless of which side(s) the matching records exist on.

Answer 2

you can also do this with a union
(SELECT
warehouse1.product.id as 1_id,
warehouse1.product.SKU,
warehouse1.product.qty as 1_qty
FROM `warehouse1`.`product`
WHERE
warehouse1.product.SKU = '$sku' )
union
(SELECT
warehouse2.product.id as 2_id ,
warehouse2.product.SKU,
warehouse2.product.qty as 2_qty
FROM `warehouse2`.`product`
WHERE warehouse2.product.SKU = '$sku' )

Answer 3

Combine your OR's in () (... OR ...):
SELECT
warehouse1.product.id as 1_id,
warehouse2.product.id as 2_id ,
warehouse1.product.SKU,
warehouse1.product.qty as 1_qty,
warehouse2.product.qty as 2_qty
FROM `warehouse1`.`product`
LEFT JOIN `warehouse2`.`product`
ON
(`warehouse1`.`product`.`SKU` = `warehouse2`.`product`.`SKU`)
WHERE (warehouse1.product.SKU = '$sku'
OR
warehouse2.product.SKU = '$sku')
ORDER BY
(1_qty + 2_qty) DESC