SQL Server 2017

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CREATE TABLE Items (
  ItemId INT,
  ComponentId INT,
  Quantity INT
)
INSERT INTO Items
SELECT ItemId=1, ComponentId=2, Quantity=11
UNION
SELECT ItemId=1, ComponentId=3, Quantity=12
UNION
SELECT ItemId=2, ComponentId=3, Quantity=13
UNION
SELECT ItemId=2, ComponentId=5, Quantity=14
UNION 
SELECT ItemId=2, ComponentId=6, Quantity=15
UNION
SELECT ItemId=3, ComponentId=4, Quantity=16
UNION
SELECT ItemId=3, ComponentId=6, Quantity=17
7 rows affected

;WITH CTE AS
(
  SELECT ItemId,
    ComponentId,
    Quantity
  FROM Items
  WHERE ItemID NOT IN (SELECT ComponentId FROM Items)
  UNION ALL
  SELECT b.ItemId,
    b.ComponentId,
    a.Quantity*b.Quantity
  FROM Items b
  INNER JOIN CTE a ON a.ComponentId = b.ItemID
)

SELECT ComponentId,
  MAX(Quantity) AS Quantity
FROM CTE
WHERE ComponentId NOT IN (SELECT ItemId FROM Items)
GROUP BY ComponentId


ComponentId
Quantity


4
2288

5
154

6
2431