>>See
>>
>>Including an Aggregated Column's Related Values
>
>Yes, the ActionDate column.

select * from (SELECT i.*, p.PartNo, p.Description, l.Location, w.WarehouseCode, w.Caption AS Warehouse, w.WarehouseId, Row_Number() over (partition by p.PartNo, w.WarenhouseCode, i.Location order by ActionDate DESC) as RowNum
	FROM Inventory i
	JOIN Parts p ON p.PartId = i.PartId
	LEFT JOIN Locations l ON l.LocationId = i.LocationId
	LEFT JOIN Warehouses w ON w.WarehouseId = i.WarehouseId
	WHERE p.PartNo = @PartNo AND
		  (@SerialNo IS NULL OR i.SerialNo = @SerialNo) AND
		  w.WarehouseId = @WarehouseId AND
		  i.LocationId IS NOT NULL AND
		  l.RemoveFromInv = 0) where RowNum = 1

This is one of the possible solutions - may be the simplest one here.