UPDATE B
SET B.[HW_PCLW]= t.HW_PCLW
FROM
(SELECT A.[HQ Partner ID],
SUM(A.[Sellout Est Net CLC]) / 
(select SUM([Sellout Est Net CLC]) 
from dbo.tbl_FlashProData 
WHERE Month>(SELECT CAST(CONVERT(VARCHAR(6), DATEADD(MONTH, DATEDIFF(MONTH, 0, SYSDATETIME()) - 13, 0), 112) AS INT)
)
) AS [HW_PCLW]
from dbo.tbl_FlashProData A  
inner join dbo.tbl_PLMapping C 
ON A.[Current Product Line] = C.PL AND C.Category='HW_PCLW' 
AND a.Month>(SELECT CAST(CONVERT(VARCHAR(6), DATEADD(MONTH, DATEDIFF(MONTH, 0, SYSDATETIME()) - 13, 0), 112) AS INT)) 
GROUP BY A.[HQ Partner ID]
) t
INNER JOIN dbo.tbl_Non_Verified_Partner B 
ON B.[SYS_ID]=A.[HQ Partner ID]