Question

我有一个包含2列（id，childId）的表，其中包含以下数据：

1,2
2,4
3,5
4,6
5，null
6，null

我有以下CTE获取记录并且工作正常。

DECLARE @id TABLE (id int, childId int);
INSERT INTO @id SELECT 1, 2;
INSERT INTO @id SELECT 2, 4;
INSERT INTO @id SELECT 3, 5;
INSERT INTO @id SELECT 4, 6;
INSERT INTO @id SELECT 5, null;
INSERT INTO @id SELECT 6, null;

WITH cte AS  
(
    SELECT id, childId
    FROM @id
    WHERE id = 1
    UNION ALL
    SELECT b.id, b.childId
    FROM @id b
    INNER JOIN cte 
        ON b.id = cte.childId
)
SELECT * FROM cte

但是，我想添加锚点详细信息，以便结果如下所示：

1,2，null
2,4,1
4,6,1
6，null，1

这样第3列就是主要的锚记录。

这可能吗？

Answer 1

char

提供测试代码：

WITH cte AS  
(
    SELECT id, childId, id AS anchorId
    FROM mytable
    WHERE 
        id IN (SELECT id FROM @id)
    UNION ALL
    SELECT b.id, b.childId, cte.anchorId
    FROM mytable b
    INNER JOIN cte 
        ON b.id = cte.childId
)
SELECT
    id
    , childId
    , case
        WHEN id = anchorId THEN NULL
        ELSE anchorId
    END as anchorId
FROM cte

Answer 2

只需在CTE中添加一个thrid列。

declare @mytable table ( id int, childId int );
insert  @mytable
        ( id, childId )
values  ( 1, 2 ),
        ( 2, 4 ),
        ( 3, 5 ),
        ( 4, 6 ),
        ( 5, null ),
        ( 6, null );
declare @id table ( id int );
insert  into @id
        select  1;
insert  into @id
        select  3;

with    cte
          as ( select   id ,
                        childId ,
                        id root
               from     @mytable
               where    id in ( select  id
                                from    @id )
               union all
               select   b.id ,
                        b.childId ,
                        cte.root
               from     @mytable b
                        inner join cte on b.id = cte.childId
             )
    select  *
    from    cte;

如何在使用CTE时获取锚点详细信息？

2 个答案: