Subquery Inner Join with Date Manipulation

SELECT     SUM(COST_15 * RUNTTL_15) AS EXT
FROM         dbo.Transaction_History AS TH
INNER JOIN
(SELECT     PRTNUM_15 AS PART, STKID_15 AS STK, CAST(MAX(CAST(CONVERT(DATE, TNXDTE_15, 120) AS CHAR(10)) + ‘ ‘ + LEFT(TNXTIM_15, 2) + ‘:’ + SUBSTRING(TNXTIM_15,
                       3, 2) + ‘:’ + RIGHT(TNXTIM_15, 2)) AS DATETIME) AS DT
FROM         dbo.Transaction_History
WHERE     (TNXCDE_15 IN (‘A’, ‘C’, ‘I’, ‘R’, ‘S’, ‘N’, ‘T’, ‘F’)) AND TNXDTE_15 < ‘2012-12-01’
GROUP BY PRTNUM_15, STKID_15) AS TH1 ON TH.PRTNUM_15 = TH1.PART AND TH.STKID_15 = TH1.STK AND
CAST(CAST(CONVERT(DATE, TH.TNXDTE_15, 120) AS CHAR(10)) + ‘ ‘ + LEFT(TH.TNXTIM_15, 2) + ‘:’ + SUBSTRING(TH.TNXTIM_15, 3, 2) + ‘:’ + RIGHT(TH.TNXTIM_15, 2) AS DATETIME)
= TH1.DT