;WITH CTE AS
(
	SELECT forumId,ParentId,HitNumber,
		Seq = CAST(','+CAST(forumId AS VARCHAR(2)) AS VARCHAR(20))
	FROM #tab1 
	WHERE ParentId IS NULL 
	UNION ALL
	SELECT DD2.forumId, DD2.ParentId, DD2.HitNumber,
		Seq = CAST(CTE.Seq + ',' + CAST(DD2.forumId AS VARCHAR(2)) AS VARCHAR(20))
	FROM #tab1 AS DD2
	INNER JOIN CTE 
		ON CTE.ForumId = DD2.parentId
)
SELECT c.forumId, c.ParentId, 
	x.TotalHitNumber  
FROM CTE c
CROSS APPLY ( 
	SELECT TotalHitNumber = SUM(HitNumber) 
	FROM CTE 
	WHERE Seq+',' LIKE '%,'+CAST(c.forumId AS VARCHAR(2))+',%'
) x
ORDER BY c.forumId