--Before
SELECT	*
FROM	@ItemMaster

-- Solution
;WITH cteYak(theCode, thePrice, theDate, recID)
AS (
	SELECT	theCode,
		thePrice,
		theDate,
		ROW_NUMBER() OVER (PARTITION BY theCode ORDER BY theDate DESC, thePrice DESC) AS recID
	FROM	(
			SELECT	item_code AS theCode,
				unitprice AS thePrice,
				rec_date AS theDate
			FROM	@GoodsReceipt

			UNION ALL

			SELECT	item_code,
				unitprice,
				reqs_date
			FROM	@ItemRequest

			UNION ALL

			SELECT	item_code,
				unitprice,
				amend_date
			FROM	@im_rq_amendment
		) AS d
)
MERGE	@ItemMaster AS tgt
USING	(
		SELECT	theCode,
			thePrice,
			theDate
		FROM	cteYak
		WHERE	recID = 1
	) AS src ON src.theCode = tgt.Item_Code
WHEN	MATCHED
		THEN	UPDATE
			SET	tgt.UnitPrice = src.thePrice,
				tgt.Price_Date = src.theDate
WHEN	NOT MATCHED BY TARGET
		THEN	INSERT	(
					Item_Code,
					UnitPrice,
					Price_Date
				)
			VALUES	(
					src.theCode,
					src.thePrice,
					src.theDate
				);

-- After
SELECT	*
FROM	@ItemMaster