CTE遞歸查詢

Question

我與員工的記錄表，顯示僱員的關係，他們舉報誰：

From_ID position   TO_ID position 
---------------------------------------- 
1   Lowest_employee 3  employee 
3   employee   4  employee 
4   employee   5  BOSS 
2   Lowest_employee 6  employee 
6   employee   3  employee 
10  Lowest_employee 50  BOSS2 

我想顯示的結果是這樣的，與員工/老闆的ID ：

EmployeeID BossID 
-------------------- 
1   5 
2   5 
10   50 

這意味着員工1和ID 5 2報告和僱員10個報告到另一個老闆ID 50.

我知道我需要使用CTE和遞歸查詢，但無法理解如何完成，我更新CTE遞歸查詢。

我讀這篇文章，但它沒有任何意義，我MS link

與實現，這將是有用的需要查詢任何幫助。

Answer 1

這包括建立測試數據，但我認爲這是你想要的東西：

測試數據：

DECLARE @Table TABLE 
(
    From_ID int, 
    TO_ID int 
) 
INSERT INTO @Table VALUES(1,3) 
INSERT INTO @Table VALUES(3,4) 
INSERT INTO @Table VALUES(4,5) 
INSERT INTO @Table VALUES(2,6) 
INSERT INTO @Table VALUES(6,3) 
INSERT INTO @Table VALUES(10,50) 

查詢得到答案：

;WITH Hierarchy (Employee, Superior, QueryLevel) 
AS 
(
    --root is all employees that have no subordinates 
    SELECT E.From_ID, E.TO_ID, 1 
    FROM @Table E 
    LEFT 
    JOIN @Table S 
      ON S.TO_ID = E.From_ID 
    WHERE S.TO_ID IS NULL 
    --recurse up tree to final superior 
    UNION ALL 
    SELECT H.Employee, S.TO_ID, H.QueryLevel + 1 
    FROM Hierarchy H 
    JOIN @Table S 
      ON S.From_ID = H.Superior 
) 
SELECT Employee, Superior 
FROM 
(
    SELECT *, ROW_NUMBER() OVER(PARTITION BY Employee ORDER BY QueryLevel DESC) AS RowNumber 
    FROM Hierarchy 
) H 
WHERE RowNumber = 1 

本質，這作品通過：

1）得到的所有員工沒有reportees（根）

2）通過凸臺遞歸起來，記錄該「等級」

3）使用上/分區只選擇「最終」老闆

Answer 2

WITH q (employee, boss) AS 
     (
     SELECT fromId, toId 
     FROM mytable 
     WHERE fromId NOT IN 
       (
       SELECT toId 
       FROM mytable 
       ) 
     UNION ALL 
     SELECT employee, toId 
     FROM q 
     JOIN mytable t 
     ON  t.fromId = boss 
     ) 
SELECT * 
FROM q 
WHERE boss NOT IN 
     (
     SELECT fromId 
     FROM mytable 
     ) 

Answer 3

你可以嘗試這樣的事情嗎？

DECLARE @Employees TABLE (
    EmployeeId INT, 
    PositionName VARCHAR(50), 
    ReportsToId INT); 
INSERT INTO @Employees VALUES (1, 'Driver', 3); 
INSERT INTO @Employees VALUES (3, 'Head of Driving Pool', 4); 
INSERT INTO @Employees VALUES (4, 'Corporate Flunky', 5); 
INSERT INTO @Employees VALUES (2, 'Window Cleaner', 6); 
INSERT INTO @Employees VALUES (6, 'Head of Office Services', 3); 
INSERT INTO @Employees VALUES (10, 'Minion', 50); 
INSERT INTO @Employees VALUES (5, 'BOSS', NULL); 
INSERT INTO @Employees VALUES (50, 'BOSS2', NULL); 
WITH Employees AS (
    SELECT 
     EmployeeId, 
     1 AS [Level], 
     EmployeeID AS [Path], 
     ISNULL(ReportsToId, EmployeeId) AS ReportsToId 
    FROM 
     @Employees 
    WHERE 
     ReportsToId IS NULL 
    UNION ALL 
    SELECT 
     e.EmployeeID, 
     x.[Level] + 1 AS [Level], 
     x.[Path] + e.EmployeeID AS [Path], 
     x.ReportsToId 
    FROM 
     @Employees e 
     INNER JOIN Employees x ON x.EmployeeID = e.ReportsToId) 
SELECT 
    ec.EmployeeId, 
    e.PositionName, 
    ec.[Level], 
    CASE WHEN ec.ReportsToId = ec.EmployeeId THEN NULL ELSE ec.ReportsToId END AS ReportsToId --Can't really report to yourself 
FROM 
    Employees ec 
    INNER JOIN @Employees e ON e.EmployeeId = ec.EmployeeId 
ORDER BY 
    ec.[Path];