Multi-statement Scalar to Multi-statement TVF - sql-server

Question

I have a question on these few lines of code, particularly how this #workTable is being populated with the StartingCost and EndingCost values:
DECLARE #workTable TABLE
(
ProductId INT ,
StartingCost MONEY ,
EndingCost MONEY
) ;
The full query is listed below.
IF OBJECT_ID(N'Production.ms_tvf_ProductCostDifference',N'TF' ) IS NOT NULL
--SELECT * FROM sys.objects WHERE name LIKE 'm%'
DROP FUNCTION Production.ms_tvf_ProductCostDifference ;
GO
CREATE FUNCTION Production.ms_tvf_ProductCostDifference
(
#StartDate DATETIME ,
#EndDate DATETIME
)
RETURNS #retCostDifference TABLE
(
ProductId INT ,
CostDifference MONEY
)
AS
BEGIN
DECLARE #workTable TABLE
(
ProductId INT ,
StartingCost MONEY ,
EndingCost MONEY
) ;
INSERT INTO #retCostDifference
( ProductId ,
CostDifference
)
SELECT ProductID ,
StandardCost
FROM ( SELECT pch.ProductID ,
pch.StandardCost ,
ROW_NUMBER() OVER
( PARTITION BY ProductID
ORDER BY StartDate DESC ) AS rn
FROM Production.ProductCostHistory AS pch
WHERE EndDate BETWEEN
#StartDate AND #EndDate
) AS x
WHERE x.rn = 1 ;
UPDATE #retCostDifference
SET CostDifference = CostDifference - StandardCost
FROM #retCostDifference cd
JOIN ( SELECT ProductID ,
StandardCost
FROM ( SELECT pch.ProductID ,
pch.StandardCost ,
ROW_NUMBER() OVER
( PARTITION BY ProductID
ORDER BY StartDate ASC )
AS rn
FROM Production.ProductCostHistory
AS pch
WHERE EndDate BETWEEN
#StartDate AND #EndDate
) AS x
WHERE x.rn = 1
) AS y ON cd.ProductId = y.ProductID ;
RETURN ; select top 20 * from Production.ProductCostHistory
END
Go
/********************************************************************************
The code above represents
Listing 17: A multi-statement TVF
This TVF, Instead of retrieving a single row from the database and calculating
the price difference, pulls back all rows from the database and calculates the
price difference for all rows at once.
*********************************************************************************/
SELECT p.ProductID ,
p.Name ,
p.ProductNumber ,
pcd.CostDifference
FROM Production.Product AS p
INNER JOIN Production.ms_tvf_ProductCostDifference
('2001-01-01', GETDATE()) AS pcd
ON p.ProductID = pcd.ProductID ;

Answer 1

In your code, the below block is simply declared and it never used.
DECLARE #workTable TABLE
(
ProductId INT ,
StartingCost MONEY ,
EndingCost MONEY
) ;
Since #retCostDifference is the return table for this function and all the transactions (INSERT, UPDATE) are happened to the #retCostDifference table only.
There is no use of #workTable in the function.