计算层次结构

Question

我有一个 table 层次结构：

CREATE TABLE mng 
(
    id INTEGER NOT NULL PRIMARY KEY, 
    name VARCHAR(50) NOT NULL,
    manager_id INTEGER
);

INSERT INTO mng (id, name, manager_id) VALUES (1, 'Lola', NULL);
INSERT INTO mng (id, name, manager_id) VALUES (2, 'Bella', NULL);
INSERT INTO mng (id, name, manager_id) VALUES (3, 'Lo', 1);
INSERT INTO mng (id, name, manager_id) VALUES (4, 'Ann', 2);
INSERT INTO mng (id, name, manager_id) VALUES (5, 'Ki', 3);
INSERT INTO mng (id, name, manager_id) VALUES (6, 'Qo', 5);

我需要打印所有高层管理人员（其中 manager_id 是 NULL）及其下属人数（包括所有级别）

   id   |   cnt
--------+---------
   1    |   3
   2    |   1

更新正在尝试这样的事情：

WITH DirectReports(ManagerID, Employee) AS   
(  
    SELECT id, 0 AS Employee  
    FROM mng 
    WHERE manager_id IS NULL  
  
    UNION ALL  
  
    SELECT e.id, Employee + 1  
    FROM mng AS e  
    INNER JOIN DirectReports AS d  
    ON e.manager_id  = d.ManagerID    
)  
SELECT ManagerID, Employee  
FROM DirectReports  
ORDER BY ManagerID;

得到了层数，但是如何得到层数？

Answer 1

首先你可以得到manager下的员工，top level manager。以后可以统计top level manager下的员工

;WITH DirectReports(EmployeeId, ManagerID, TopMostManagerId) AS   
(  
    SELECT id, Null, id 
    FROM #mng 
    WHERE manager_id IS NULL  
  
    UNION ALL  
  
    SELECT e.id, e.manager_Id, d.TopMostManagerId  
    FROM #mng AS e  
    INNER JOIN DirectReports AS d  
    ON e.manager_id  = d.EmployeeId    
)  
SELECT TopMostManagerId, COUNT(EmployeeId) as CountOfEmployees
FROM DirectReports 
WHERE ManagerID is not null -- excludes toplevel manager
group by TopMostManagerId

TopMostManagerId	CountOfEmployees
1	3
2	1

Answer 2

您的原始代码的问题是您忘记了“最高管理者”。但是，您可以将其保留在 CTE 中，并简单地为每个员工列出它：

WITH DirectReports(id, TopMgr, ManagerID, Employee) AS   
(  
    SELECT id, id, NULL, 0 AS Employee
    FROM mng 
    WHERE manager_id  IS NULL  
  
    UNION ALL  
  
    SELECT e.id, d.TopMgr, e.manager_id, 1 AS Employee
    FROM mng AS e  
    INNER JOIN DirectReports AS d  
    ON e.manager_id  = d.id   
)  
SELECT TopMgr, SUM(Employee)
FROM DirectReports  
GROUP BY TopMgr
ORDER BY TopMgr

输出：

    TopMgr  EmployeeCount
1   3
2   1

计算层次结构

Counting the hierarchy

sql

sql-server

hierarchy