在SQL層次結構中顯示所有子孫級CTE

Question

我在SQL Server中有一個層次結構，有多個父級，但似乎無法獲得我需要的結果集。

這就是我到目前爲止。

DECLARE @Table TABLE (ChildId varchar(max), ParentId varchar(max)) 
INSERT INTO @Table (ChildId,ParentId) 
VALUES 
     ('England',NULL), 
     ('Cities',NULL), 
     ('Towns',NULL), 
     ('South West','England'), 
     ('Bristol','South West'), 
     ('Bristol','Cities'), 
     ('Suburb','Bristol'), 
     ('Thornbury','South West'), 
     ('Thornbury','Towns'); 


WITH CTE (ChildId, ParentId, Level) 
AS ( 
     SELECT 
      ChildId, 
      ParentID, 
      0 
     FROM @Table 
     WHERE ParentID IS NULL 
     UNION ALL 

     SELECT 
      r.ChildId, 
      r.ParentId, 
      ct.Level + 1 
     FROM @Table r 
     JOIN CTE ct 
     ON ct.ChildId = r.ParentId 

    ) 

SELECT * FROM CTE order by childId, level 

，給了我這樣的結果集：

ChildId | ParentId | Level 
Bristol | Cities  | 1 
Bristol | South West | 2 
Suburb  | Bristol | 2 
Suburb  | Bristol | 3 
Cities  | NULL  | 0 
England | NULL  | 0 
South West | England | 1 
Thornbury | Towns  | 1 
Thornbury | South West | 2 
Towns  | NULL  | 0 

但我也想祖父母和偉大的祖父母和偉大的祖父母（等）：

ChildId | ParentId | Level 
Bristol | Cities  | 1 
Bristol | South West | 2 
Bristol | England | <------------------------ 
Suburb  | South West | <------------------------ 
Suburb  | England | <------------------------ 
Suburb  | Cities  | <------------------------ 

等

Answer 1

什麼你正在嘗試做的似的，至少在一定程度上，阮岡納讚的分類。在這種情況下，你必須在層次結構上，不下來：

with cte as (
    select t.ChildId, t.ParentId, 0 as [Lvl] 
    from @Table t 
    where t.ParentId is not null 
    union all 
    select c.ChildId, t.ParentId, c.Lvl + 1 
    from @Table t 
     inner join cte c on c.ParentId = t.ChildId 
    where t.ParentId is not null 
) 
select * from cte c order by c.ChildId, c.Lvl, c.ParentId; 

編輯：在CTE的遞歸部分更新WHERE條款。看起來像是從最初的嘗試剩下的一些，我忘了想通過..

Answer 2

如何使用遞歸表值函數而不是CTE：

CREATE FUNCTION tvf_GetParents 
( 
    @childID VARCHAR(MAX), 
    @level INT 
) 
RETURNS 
@output TABLE 
(
    ancestor VARCHAR(MAX), 
    level INT 
) 
AS 
BEGIN 

    DECLARE @parentIDs TABLE (pID VARCHAR(MAX)) 

    -- Get parent of child and add it to output 
    IF EXISTS (SELECT 1 FROM HTable WHERE ChildId = @childID AND ParentId IS NOT NULL) 
    BEGIN 
     INSERT @parentIDs 
     SELECT ParentId FROM HTable WHERE ChildId = @childID 

     INSERT INTO @output (ancestor, level) 
     SELECT pID, @level FROM @parentIDs 
    END  
    ELSE 
     RETURN 

    DECLARE @pID VARCHAR(MAX) = 0 

    -- Iterate over all parents (cursorless loop) 
    WHILE (1 = 1) 
    BEGIN 

     -- Get next ParentId 
     SELECT TOP 1 @pID = pID 
     FROM @parentIDs 
     WHERE pID > @pID 
     ORDER BY pID 

     -- Exit loop if no more parents 
     IF @@ROWCOUNT = 0 BREAK; 

     -- call function recursively so as to add to output 
     -- the rest of the ancestors (if any) 
     INSERT INTO @output (ancestor, level) 
     SELECT ancestor, level FROM tvf_GetParents(@pID, @level + 1) 
    END 

    RETURN 
END 
GO 

使用上述功能，您可以輕鬆地獲得所有子 - 祖先對：

SELECT DISTINCT ChildId, ancestor, level 
FROM HTable h 
OUTER APPLY tvf_GetParents(h.ChildId, 0) AS p 
ORDER BY ChildId, Level 

輸出：

ChildId ancestor  level 
------------------------------ 
Bristol Cities  0 
Bristol South West 0 
Bristol England  1 
Cities  NULL   NULL 
England NULL   NULL 
South West England  0 
Suburb  Bristol  0 
Suburb  Cities  1 
Suburb  South West 1 
Suburb  England  2 
Thornbury South West 0 
Thornbury Towns  0 
Thornbury England  1 
Towns  NULL   NULL 

請注意， '等級' 有不同的含義在這裏：水平NULL表示無父母子女，等級0表示父母親記錄，等級1表示子女祖父母記錄等等。

請注意，就sql server中的遞歸函數的嵌套級別而言，存在限制。我認爲它是32.如果你的樹深度超出了這個範圍，那麼我提出的解決方案將無法工作。

Answer 3

這是你在找什麼？

WITH CTE (ChildId, FirstChild, ParentId, Level) 
AS ( 
     SELECT 
      ChildId, 
      ChildId as FirstChild, 
      ParentID, 
      0 
     FROM @Table 
     WHERE ParentID IS NULL 
     UNION ALL 
     SELECT 
      r.ChildId, 
      ct.FirstChild, 
      r.ParentId, 
      ct.Level + 1 
     FROM @Table r 
     JOIN CTE ct 
     ON ct.ChildId = r.ParentId 

    ) 
SELECT ChildId, 
    ParentId, 
    Level 
FROM CTE 
UNION 
SELECT FirstChild, 
    ParentId, 
    Level 
FROM CTE 
ORDER BY ChildId, 
    Level, 
    ParentId 

輸出：

ChildId  ParentId  Level 
-------  --------  ----- 
Bristol  Cities  1 
Bristol  South West 2 
Cities  NULL   0 
Cities  Cities  1 
Cities  Bristol  2 
England  NULL   0 
England  England  1 
England  South West 2 
England  Bristol  3 
South West England  1 
Suburb  Bristol  2 
Suburb  Bristol  3 
Thornbury Towns  1 
Thornbury South West 2 
Towns  NULL   0 
Towns  Towns  1