分层表和最高级别

Question

我在sql中使用以下函数来获取我的节点级别，但目前我的节点变得超过20000，所以运行此函数需要50秒，我该如何优化它？

   WITH cteLevels
AS
(
SELECT
  TopicId
  ,ParentId

  ,1        AS [Level]
FROM   Accounting.Topics
WHERE parentId = 0 


UNION ALL

SELECT
  Accounting.Topics.topicId
  ,Accounting.Topics.Parentid
   ,[Level] + 1 AS [Level]
 FROM   Accounting.Topics

       INNER JOIN cteLevels
         ON ( Accounting.Topics.ParentId = cteLevels.TopicID ) 

)

-- Viewing Data
SELECT
  *
FROM   cteLevels