在层次

Question

SQL顶级父记录我有一个表结构：

CompanyID，公司名称，LinkedCompanyID

使多个企业能在一个层次链接

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 

我想查询返回每个公司

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表达式采取一脸的顶级父，但所有的例子我可以从父母而不是最上面的父母中找到返回分层列表。

大家能否请提供任何指针或样本查询

Answer 1

这仍然可以用递归CTE实现：

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

试试这个：

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