如何在使用CTE时设置订单？

Question

我有一个2列（id，childId）表。数据如下：

• 1,2
• 3,4
• 2，空
• 4，空

我使用的CTE，使得我得到的子女记录：

DECLARE @id TABLE (id int); 
INSERT INTO @id SELECT 1; 
INSERT INTO @id SELECT 3; 

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

结果总是回来为：

• 1，2
• 3，4
• 4，空
• 2，空

但我需要的结果是这样的：

• 1，2
• 2，null
• 3，4，
• 4，空

即，第一锚定记录，则记录为每个锚记录递归SQL。

这可能吗？

Answer 1

将静态值添加到锚查询中。然后在递归部分添加一个大于锚查询的静态值的静态值。现在Order by

使用静态值试试这个

WITH cte AS 
(
    SELECT 0 as rn, id, childId 
    FROM mytable 
    WHERE 
     id IN (SELECT id FROM @id) 
    UNION ALL 
    SELECT 1 as rn,b.id, b.childId 
    FROM mytable b 
    INNER JOIN cte 
     ON b.id = cte.childId 
) 
SELECT * FROM cte 
Order by rn,id 

也可以考虑加入option(Maxrecursion N)。默认情况下，它只是让只100递归

Answer 2

通过增加一个序列，结果将显示在正确的顺序/嵌套

DECLARE @id TABLE (id int); 
INSERT INTO @id SELECT 1; 
INSERT INTO @id SELECT 3; 

WITH cte AS 
(
    SELECT id, childId 
      ,Seq = cast(100000+Row_Number() over (Order by id) as varchar(500)) 
    FROM mytable 
    WHERE 
     id IN (SELECT id FROM @id) 
    UNION ALL 
    SELECT b.id, b.childId 
      ,Seq = cast(concat(cte.Seq,'.',100000+Row_Number() over (Order by b.id)) as varchar(500)) 
    FROM mytable b 
    INNER JOIN cte 
     ON b.id = cte.childId 
) 
SELECT * FROM cte 
Order By Seq