CREATE Procedure CustomerAlsoBought
  (
      @ProductID int
  )
  As

  /* We want to take the top 5 products contained in
      the orders where someone has purchased the given Product */
  SELECT  TOP 5 
      OrderDetails.ProductID,
      Products.ModelName,
      SUM(OrderDetails.Quantity) as TotalNum

  FROM    
      OrderDetails
    INNER JOIN Products ON OrderDetails.ProductID = Products.ProductID

  WHERE   OrderID IN 
  (
      /* This inner query should retrieve all orders that have contained the productID */
      SELECT DISTINCT OrderID 
      FROM OrderDetails
      WHERE ProductID = @ProductID
  )
  AND OrderDetails.ProductID != @ProductID 

  GROUP BY OrderDetails.ProductID, Products.ModelName 

  ORDER BY TotalNum DESC

  GO

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