Query AND and not OR using WHERE IN (list) - sql

Question

Considering I have three tables:
product
shop
supplier
and their junction tables:
product_shop
product_supplier
I am trying to get all products that are supplied by a specific supplier and available in multiple shops, i.e. all products from supplier A that are in shop 1 and 2.
If we assume, supplier has 10 products, of which 5 are available in shop 1 and 7 are available in shop 2, but only 3 are available in shop 1 and 2, then those are the 3 I am seeking.
Here is what I have so far (in postgresql 9.6), which simulates an inclusive IN. Which works, but it doesn't seem right (proper) to me:
edit:
I use this query dynamically and have therefor to pass the list of shops (which varies), the supplier of course, and the count (which is equal to the length of the list of shops). It's not that this is a bother, but I was nonetheless wondering if there is a way to create a query using only joins.
SELECT
product_shop.product
FROM
(SELECT product FROM product_shop where shop in (1, 2)) product_shop JOIN
product_supplier ON product_shop.product = product_supplier.product
WHERE
product_supplier.supplier = A
GROUP BY
product_shop.product
HAVING
count(product_shop.product) = 2
Is there a better query to achieve the result I am seeking?
*Not a native speaker

Answer 1

I believe this will give you the desired result
SELECT product.* FROM product
JOIN product_supplier ON product.id = product_supplier.productId
JOIN product_shop ON product.id = product_shop.productId
WHERE product_shop.shopId IN (1 , 2)
AND product_supplier.supplierId = 'A'
GROUP BY product.id
HAVING COUNT(product.id) > 1
Its basically equivalent, but you do not need the subquery. There is, however, an error.
With your query you will only get the products that are available in exactly 2 shops.
since you wrote:
I am trying to get all products that are supplied by a specific supplier and available in multiple shops
Using HAVING COUNT(product.id) > 1 would be more generic and correct.
However, it would not make any difference in this case, since you restricted the search to 2 shops.
I Also changed references like product_supplier.supplier to product_supplier.supplierId. You shroud use Id fields for table relationships.

Answer 2

Here is the query with out Having the count
with cte_product -- fetching all the products which are in shop 1&2
(
SELECT product,count(product) as cnt FROM product_shop
where shop in (1, 2)
group by product
)
SELECT *
FROM
cte_product psh
JOIN
product_supplier psu
ON psh.product = psu.product
WHERE
psu.supplier = A
and psh.cnt > 1;