SQL N To No Releationship Table - sql

Question

I have 3 table by this names
Supplier :For store supplier info
SupplierID
Name
1
Supplier 1
2
Supplier 2
3
Supplier 3
4
Supplier 4
Product : For store product info
ProductID
Name
1
Product 1
2
Product 2
3
Product 3
4
Product 4
5
Product 5
SupplierProduct : For store Product that supplier can supply
ProductID
SupplierID
2
1
3
1
4
1
2
2
3
2
4
2
3
3
4
3
1
4
2
4
4
4
I want to write a query that get a bunch of product ID and return the supplier ID that have all this product ID (N:N Relation) for example get product ID 2,3 and return just supplier ID 1,2

Answer 1

This is a question of Relational Division With Remainder, with multiple divisors.
Firstly, to be able to make good solutions for this, you need your input data in tabular form. You can use a table variable or a Table Valued Parameter for this.
There are many solutions. Here is one common one:
Join the input data to the SupplierProduct table. In your case, you only want the Supplier data, so do this in a subquery.
Group it up and check that the count matches the total count of inputs
DECLARE #ProductInput TABLE (ProductID int);
INSERT #ProductInput (ProductID) VALUES (2),(3);
SELECT *
FROM Supplier s
WHERE (SELECT COUNT(*)
FROM SupplierProduct sp
JOIN #ProductInput pi ON pi.ProductID = sp.ProductID
WHERE sp.SupplierID = s.SupplierID
) = (SELECT COUNT(*) FROM #ProductInput)
;
db<>fiddle
Another common solution is a double NOT EXISTS. This verifies that there are no inputs which do not have a match. It is generally considered to be less efficient.
DECLARE #ProductInput TABLE (ProductID int);
INSERT #ProductInput (ProductID) VALUES (2),(3);
SELECT *
FROM Supplier s
WHERE NOT EXISTS (SELECT 1
FROM #ProductInput pi
WHERE NOT EXISTS (SELECT 1
FROM SupplierProduct sp
WHERE pi.ProductID = sp.ProductID
AND sp.SupplierID = s.SupplierID
)
);

Answer 2

You can use intersect as follows:
select distinct SupplierID
from SupplierProduct
where ProductID = 2
intersect
select SupplierID
from SupplierProduct
where ProductID = 3
Fiddle

Answer 3

Try this:
DECLARE #Supplier TABLE (SupplierID int, Name varchar(50));
INSERT INTO #Supplier VALUES
(1, 'Supplier 1')
, (2, 'Supplier 2')
, (3, 'Supplier 3')
, (4, 'Supplier 4')
;
DECLARE #Product TABLE (ProductID int, Name varchar(50));
INSERT INTO #Product VALUES
(1, 'Product 1')
, (2, 'Product 2')
, (3, 'Product 3')
, (4, 'Product 4')
, (5, 'Product 5')
;
DECLARE #SupplierProduct TABLE (ProductID int, SupplierID int);
INSERT INTO #SupplierProduct VALUES
(2, 1)
, (3, 1)
, (4, 1)
, (2, 2)
, (3, 2)
, (4, 2)
, (3, 3)
, (4, 3)
, (1, 4)
, (2, 4)
, (4, 4)
;
DECLARE #ProductSelection TABLE (ProductID int)
INSERT INTO #ProductSelection
SELECT
ProductID
FROM #Product
WHERE 1=1
-- AND ProductID IN (2, 3) -- returns Suppliers 1, 2
-- AND ProductID IN (3, 4) -- returns Suppliers 1, 2, 3
AND ProductID IN (2, 4) -- returns Suppliers 1, 2, 4
;
WITH SupplierList AS
(
SELECT
RowNo = ROW_NUMBER() OVER (PARTITION BY SP.SupplierID ORDER BY SP.SupplierID)
, S.SupplierID
FROM #SupplierProduct SP
JOIN #ProductSelection P ON P.ProductID = SP.ProductID
JOIN #Supplier S ON S.SupplierID = SP.SupplierID
)
SELECT
SupplierID
FROM SupplierList
WHERE RowNo = (SELECT SUM(1) FROM #ProductSelection)