Isso é semelhante ao meu pergunta .
Conforme apontado na resposta de @Origin, este é um problema de cobertura definida e é um NP-Complete problema, ou seja, incomputável para qualquer um, mas um número muito pequeno de possibilidades.
Para o seu problema, uma solução de algoritmo guloso pode ser adequada.
Não tenho tempo para resolver seu problema, mas postei abaixo o código que usei para resolver o meu. Sua estrutura de tabela é mais simples, então sua solução também deve ser!
DECLARE @GreedySetCover table
(
Location_Id int
,Supplier_Id int
,Ranking int
)
INSERT INTO @GreedySetCover
--Include Suppliers who are sole suppliers for any item
SELECT ss.Location_Id
,si.Supplier_Id
,0 Ranking
FROM (
SELECT pr.Location_Id
,pr.Item_Id
FROM PartsRequests pr
INNER JOIN
SupplierItems si ON pr.Item_Id=si.Item_Id
WHERE pr.Order_Id IS NULL
GROUP BY pr.Location_Id
,pr.Item_Id
HAVING COUNT(*)=1
) ss
INNER JOIN
SupplierItems si ON si.Item_Id=ss.Item_Id
UNION
--Include suppliers who do not charge a delivery fee
SELECT pr.Location_Id
,si1.Supplier_Id
,0 Ranking
FROM PartsRequests pr
INNER JOIN
SupplierItems si1 ON si1.Item_Id=pr.Item_Id
WHERE pr.Order_Id IS NULL
AND
(
NOT EXISTS
(SELECT ISNULL(si2.AmountPerOrder,0)
FROM SupplierItems si2
WHERE si1.Supplier_Id=si2.Supplier_Id
AND
si2.Item_Id=0)
OR
(SELECT ISNULL(si2.AmountPerOrder,0)
FROM SupplierItems si2
WHERE si1.Supplier_Id=si2.Supplier_Id
AND
si2.Item_Id=0
)=0
)
DECLARE @Ranking int = 1
--While any item does not have a supplier
WHILE EXISTS
(
SELECT pr.Location_Id
,pr.Item_Id
FROM PartsRequests pr
EXCEPT
(
SELECT gsc.Location_Id
,pr1.Item_Id
FROM @GreedySetCover gsc
INNER JOIN
SupplierItems si ON gsc.Supplier_Id=si.Supplier_Id
INNER JOIN
PartsRequests pr1 ON pr1.Item_Id=si.Item_Id AND pr1.Location_Id=gsc.Location_Id
WHERE pr1.ORDER_ID IS NULL
)
)
BEGIN
--Get the supllier whcovere uncovered items at the lowest cost
INSERT INTO @GreedySetCover
SELECT sort.Location_Id
,sort.Supplier_Id
,@Ranking
FROM (
SELECT uncovered.Location_Id
,si.Supplier_Id
,ROW_NUMBER() OVER
(PARTITION BY uncovered.Location_Id
ORDER BY
--This is the weighting function
SUM(uncovered.Quantity*si.Price) + --The cost of the Items
(SELECT ISNULL(si2.AmountPerOrder,0) --Plus the delivery fee
FROM SupplierItems si2
WHERE si.Supplier_Id=si2.Supplier_Id
AND
si2.Item_Id=0)
/cast(COUNT(*) as float)) RowNum --Divided by the number of items covered
FROM (
SELECT pr.Location_Id
,pr.Item_Id
,pr.Quantity
FROM PartsRequests pr
--Remove uncovered items
EXCEPT
(
SELECT gsc.Location_Id
,pr1.Item_Id
,pr1.Quantity
FROM @GreedySetCover gsc
INNER JOIN
SupplierItems si ON gsc.Supplier_Id=si.Supplier_Id
INNER JOIN
PartsRequests pr1 ON pr1.Item_Id=si.Item_Id AND pr1.Location_Id=gsc.Location_Id
WHERE pr1.ORDER_ID IS NULL
)
) uncovered
INNER JOIN
SupplierItems si ON si.Item_Id=uncovered.Item_Id
GROUP BY Location_Id, Supplier_Id
) sort
WHERE RowNum = 1
SET @[email protected]+1
END
--SELECT *
--FROM @GreedySetCover
--ORDER BY Ranking
-- ,Location_Id
SELECT Location_Id
,Supplier_Id
,Number
,Quantity
,Price
FROM (
SELECT pr.Id PartsRequest_Id
,pr.Item_Id
,pr.Quantity
,pr.RequestTime
,pr.Location_Id
,pr.Person_Id
,pr.Order_Id
,si.Supplier_Id
,si.Number
,si.Price
,si.AmountPerOrder
,ROW_NUMBER() OVER (PARTITION BY gsc.Location_Id,pr.Item_Id
ORDER BY si.Price) RowNum
FROM @GreedySetCover gsc
INNER JOIN
PartsRequests pr ON gsc.Location_Id=pr.Location_Id
INNER JOIN
SupplierItems si ON gsc.Supplier_Id=si.Supplier_Id
AND
pr.Item_Id=si.Item_Id
) Results
WHERE RowNum=1
UNION
SELECT gsc.Location_Id
,si.Supplier_Id
,si.Number
,si.AmountPerOrder
,Price
FROM @GreedySetCover gsc
INNER JOIN
SupplierItems si ON gsc.Supplier_Id=si.Supplier_Id
WHERE AmountPerOrder>0
ORDER BY Location_Id
,Supplier_Id
,Number
