Question

鉴于下表：

create table TreeNode
(
  ID int not null primary key,
  ParentID int null foreign key references TreeNode (ID)
)

如何编写公共表表达式以从根开始（WHERE ParentID IS NULL）并遍历其后代，直到结果集包含某个目标节点（例如，WHERE ID = n）？很容易从目标节点开始并向上遍历到根，但这不会生成相同的结果集。具体而言，不包括与目标节点具有相同父节点的节点。

我的第一次尝试是：

with Tree as
(
  select
    ID,
    ParentID
  from
    TreeNode
  where
    ParentID is null
  union all select
    a.ID,
    a.ParentID
  from
    TreeNode a
    inner join Tree b
      on b.ID = a.ParentID
  where
    not exists (select * from Tree where ID = @TargetID)
)

出现错误：Recursive member of a common table expression 'Tree' has multiple recursive references.

注意：我只对自上而下的遍历感兴趣。

Answer 1

更新2：

第三次尝试在两个方向上“遍历”树。

从ParentIDs到Target建立所有root的CTE。然后，选择tree nodes或ID在短名单中显示的Parent。

--
;
WITH    Tree
          AS ( SELECT   ID
                       ,ParentID
               FROM     TreeNode
               WHERE    [ID] = @targetId
               UNION ALL
               SELECT   a.ID
                       ,a.ParentID
               FROM     TreeNode a
                        INNER JOIN Tree b ON b.ParentID = a.ID
             )
    SELECT  *
    FROM    [dbo].[TreeNode] n
    WHERE  EXISTS (SELECT *
                   FROM [Tree] t
                   WHERE [t].[ID] = [n].[ID]
                         OR [t].[ID] = [n].[ParentID]
                  )

一旦结果集包含某个值，就退出递归公用表表达式

1 个答案: