Question

我有一张叫雇员的表。请参考下表，我希望员工向哪个经理报告的级别。我不知道会有什么逻辑。我已经使用过CTE，但没有得到预期的结果。在这种情况下，请帮助我以获得预期的结果。

表员工

EmpID.                     EmpName.                         ManagerID
1                             A                                Null
2                             B                                  1
3                             C                                  1
4                             D                                  2
5                             E                                  3
6                             F                                  4
7                             G                                  5
8                             H                                  5

预期结果

EmpName.                      ManagerName                         Level
A                                Null                                1
B                                  A                                 2
C                                  A                                 2
D                                  B                                 3
E                                  C                                 4
F                                  D                                 5
G                                  E                                 6
H                                  E                                 6

Answer 1

假设您正在使用Sql Server，则可以使用以下代码进行操作：

WITH cte (EmpId, EmpName, ManagerName, LEVEL) AS (
SELECT EmpId, EmpName, CAST('' AS VARCHAR) as ManagerName, 1 AS LEVEL
FROM Employee
WHERE ManagerId IS NULL

UNION ALL

SELECT e1.EmpId, e1.EmpName, CAST(cte.EmpName AS VARCHAR) ManagerName, (cte.LEVEL + 1) AS LEVEL
FROM Employee e1
    JOIN cte ON e1.ManagerId = cte.EmpId    
)

SELECT EmpName, ManagerName, LEVEL FROM cte
ORDER BY EmpName

请注意，您需要修改预期输出中的级别。例如，对于员工H，层次结构为H => E => C => A，这表明其级别为4。正确的级别如下：

EmpName  ManagerName  Level    
A                     1
B        A            2
C        A            2
D        B            3
E        C            3
F        D            4
G        E            4
H        E            4

Answer 2

递归CTE在Postgresql中工作。

一旦获得了每个员工的所有级别，就可以将其分组以获取最大级别。

WITH RECURSIVE RCTE AS
( 
    SELECT 
     EmpID AS BaseEmpID, 
     ManagerID AS BaseManagerID,
     1 AS Lvl, 
     EmpID, 
     ManagerID
    FROM employee

    UNION ALL

    SELECT 
     c.BaseEmpID,
     c.BaseManagerID,
     Lvl + 1,
     m.EmpID,
     m.ManagerID
    FROM RCTE c
    JOIN employee m 
      ON m.EmpID = c.ManagerID
)
, EMPLEVELS AS
(
    SELECT 
     BaseEmpID, 
     BaseManagerID, 
     MAX(Lvl) AS Level
    FROM RCTE
    GROUP BY BaseEmpID, BaseManagerID
)
SELECT 
 e.EmpName, 
 m.EmpName AS ManagerName,
 elvl.Level
FROM EMPLEVELS elvl
JOIN employee e ON e.EmpID = elvl.BaseEmpID
LEFT JOIN employee m ON m.EmpID = elvl.BaseManagerID
ORDER BY elvl.BaseEmpID;

返回：

empname managername level
A       NULL        1
B       A           2
C       A           2
D       B           3
E       C           3
F       D           4
G       E           4
H       E           4

如果删除了RECURSIVE单词，则该查询将在MS Sql Server中工作。

Answer 3

我认为您想要一个简单的join：

select e.name, em.name as manager_name
from employees e left join
     employees em
     on e.managerId = em.empId;

SQL查询从一张表中获取组织级别的层次结构

3 个答案: