WITH result (Id, ParentId, Category, Num)
AS
(
	SELECT 1, 0, '分类1', 0
	UNION ALL
	SELECT 2, 1, '分类1-1',10
	UNION ALL
	SELECT 3, 1, '分类1-2', 10
	UNION ALL
	SELECT 4, 3, '分类1-2-1', 5 
	UNION ALL
	SELECT 5, 0, '分类2', 5 
	UNION ALL
	SELECT 6, 0, '分类3', 5 
	UNION ALL
	SELECT 7, 6, '分类3-1', 5 
	UNION ALL
	SELECT 8, 4, '分类1-2-1-1', 5 
),

CTE(Id, ParentId, Category, Path, Num)
As
(
  SELECT A.Id, A.ParentId, A.Category, CAST(A.Id As VARCHAR(MAX))+'->',A.Num 
  FROM result A 
  WHERE A.ParentId = 0
  UNION ALL
  SELECT B.Id, B.ParentId, B.Category,C.Path+CAST(B.Id As VARCHAR(MAX)) + '->', B.Num 
  FROM result B
  INNER JOIN CTE c on C.Id = B.ParentId
)
--SELECT * FROM CTE
SELECT C.Id,
C.Category,
SUM(C1.Num) AS Num
FROM CTE AS C
--整个统计方法的核心就是这一句代码：CHARINDEX
INNER JOIN CTE AS C1 ON CHARINDEX(C.Path, C1.Path) = 1
GROUP BY C.ID,C.Category