在層次

Question

SQL頂級父記錄我有一個表結構：

CompanyID，公司名稱，LinkedCompanyID

使多個企業能在一個層次鏈接

例如

CompanyID, CompanyName, LinkedCompanyID 
1   Company A, NULL 
2   Company B, 1 
3   Company C, 2 
4   Company D, 2 
5   Company E, 4 
6   Company F, 3 
7   Company G, NULL 

我想查詢返回每個公司

即

CompanyID, CompanyName, ToplevelParentID 
1   Company A, NULL (or 1 I don't mind) 
2   Company B, 1 
3   Company C, 1 
4   Company D, 1 
5   Company E, 1 
6   Company F, 1 
7   Company G, NULL (or 7 I don't mind) 

我在使用recusive CTE表達式採取一臉的頂級父，但所有的例子我可以從父母而不是最上面的父母中找到返回分層列表。

大家能否請提供任何指針或樣本查詢

Answer 1

這仍然可以用遞歸CTE實現：

CREATE TABLE #Test (CompanyID INT, CompanyName VARCHAR(20), LinkedCompanyID INT) 
INSERT INTO #Test 
SELECT 1, 'Company A', NULL UNION 
SELECT 2, 'Company B', 1 UNION 
SELECT 3, 'Company C', 2 UNION 
SELECT 4, 'Company D', 2 UNION 
SELECT 5, 'Company E', 4 UNION 
SELECT 6, 'Company F', 3 UNION 
SELECT 7, 'Company G', NULL 

;WITH CTE AS 
( SELECT *, 0 [Level] 
    FROM #Test 
    UNION ALL 
    SELECT CTE.CompanyID, CTE.CompanyName, #Test.LinkedCompanyID, Level + 1 
    FROM CTE 
      INNER JOIN #Test 
       ON CTE.LinkedCompanyID = #Test.CompanyID 
    WHERE #Test.LinkedCompanyID IS NOT NULL 
) 

SELECT c.CompanyID, c.CompanyName, c.LinkedCompanyID 
FROM ( SELECT *, MAX([Level]) OVER (PARTITION BY CompanyName) [MaxLevel] 
      FROM CTE 
     ) c 
WHERE MaxLevel = Level 

DROP TABLE #Test 

Answer 2

試試這個：

Select * , (select CompanyName from Company C_aux where C_Main.LinkedCompanyID = C_aux.CompanyID) as ToplevelParentID 
from Company C_Main