SQL-subquery workaround to join based on alias - sql

Question

Attempted Subquery using alias
SELECT
*,
IQ.EndPart,
IQ.QtyToShip
FROM
parts p
INNER JOIN (
select
*,
(case when c.kitno is null then l.partno else c.partno end) as [EndPart],
(case when c.kitno is null then l.TotalQuantity else c.reqqty end) as [QtyToShip]
FROM
shipments s
INNER JOIN shipments_li l ON s.ShipmentNo = l.ShipmentNo
LEFT JOIN ProductConfiguration c ON l.PartNo = c.KitNo WHERE s.Status='N' and year(s.OrderDate)>2007
) IQ ON p.partno = IQ.EndPart
Looking for a way to join the parts table to my query below, using the part # which is aliased as EndPart. If there is another way to acheive the results of taking two columns and combining them instead of case and an alias that would be a great alternative as well. All my searches of other individuals quest to achieve the same have yielded the result you cannot perform a join based on alias because the results have not been determined at that point, recommending a subquery as a workaround. I'm just not sure how to acheive working results. The above query was what I attempted to get working. Any help appreciated. Thanks in advance.
Original Query
SELECT
*,
(case when c.kitno is null then l.partno else c.partno end) as [EndPart],
(case when c.kitno is null then l.TotalQuantity else c.reqqty end) as [QtyToShip]
FROM
shipments s
INNER JOIN shipments_li l ON s.ShipmentNo = l.ShipmentNo
LEFT JOIN ProductConfiguration c ON l.PartNo = c.KitNo
WHERE
s.Status='N'
and year(s.OrderDate)>2007
order by s.shipmentno

Answer 1

More proper way
--- CREATE TempTable
DECLARE #tblTemp AS TABLE (EndPart INT,
QtyToShip INT)
INSERT INTO #tblTemp (EndPart, QtyToShip)
SELECT
(CASE WHEN c.kitno IS NULL
THEN l.partno ELSE c.partno END) AS [EndPart],
(CASE WHEN c.kitno IS NULL
THEN l.TotalQuantity
ELSE c.reqqty END) AS [QtyToShip]
FROM dbo.Shipments s WITH(NOLOCK)
INNER JOIN shipments_li l WITH(NOLOCK) ON s.ShipmentNo = l.ShipmentNo
LEFT JOIN ProductConfiguration c WITH(NOLOCK) ON l.PartNo = c.KitNo
WHERE s.Status='N' AND YEAR(s.OrderDate)>2007
SELECT
p.*,
tmp.EndPart,
tmp.QtyToShip
FROM dbo.parts p WITH(NOLOCK)
INNER JOIN #tblTemp tmp ON p.partno = tmp.EndPart