如何找到一條記錄的第n個孩子在SQL查詢

Question

我有存儲類別和子類別（自聯接）

The table structure is like this: 
-CategoryId 
-CategoryName 
-ParentCategoryId 

如何找到在SQL查詢的類別的第n個孩子/孩子的桌子

Answer 1

如何使這樣的方法

DECLARE @Categories TABLE(
     CategoryId INT, 
     CategoryName VARCHAR(20), 
     ParentCategoryId INT 
) 

INSERT INTO @Categories SELECT 1, '1',NULL 
INSERT INTO @Categories SELECT 2, '2',NULL 

INSERT INTO @Categories SELECT 3, '1.3',1 
INSERT INTO @Categories SELECT 4, '1.4',1 

INSERT INTO @Categories SELECT 5, '1.3.5',3 
INSERT INTO @Categories SELECT 6, '1.3.6',3 
INSERT INTO @Categories SELECT 7, '1.3.6.7',6 

INSERT INTO @Categories SELECT 8, '1.4.8',4 

DECLARE @CatID INT, 
     @NthLevel INT 
SELECT @CatID = 1, 
     @NthLevel = 2 

;WITH Vals AS (
     SELECT *, 
       1 AS CatLevel 
     FROM @Categories c 
     WHERE CategoryId IS NULL 
     UNION ALL 
     SELECT c.*, 
       CatLevel + 1 AS CatLevel 
     FROM Vals v INNER JOIN 
       @Categories c ON c.ParentCategoryId = v.CategoryID 
) 
SELECT * 
FROM Vals 
WHERE CatLevel = @NthLevel 

這將遞歸地構建樹結構，並將其限制在您正在查找的樹級別上。

Answer 2

SELECT ParentCategoryId, 
    , CategoryId AS [n-th child] 
FROM (
    SELECT CategoryId 
    , ParentCategoryId 
    , ROW_NUMBER() OVER (PARTITION BY ParentCategoryId ORDER BY CategoryId) as ChildNumber 
    FROM Categories 
) p 
WHERE ChildNumber = %N 

Answer 3

要找到N個孩子，通過類別編號排序，M類：

select * 
from (
     select row_number() over (order by c.CategoryId) as rn 
     ,  c.* 
     from Categories p 
     join Categories c 
     on  p.CategoryId = c.ParentCategoryId 
     where p.CategoryId = M 
     ) 
where rn = N