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Sql Server: CTE Recursive Query to Get Employee Manager Hierarchy with Level

Introduction: In this article I have explained How to get parent child hierarchical relationship with levels using CTE (Common Table Expression) recursive query in sql.


Description: While working with database we often store parent and child id in same table. For example Category and sub category Id, Employee and his manager id etc. Here in this article I am taking an example where employees and their manager are stored in same table. And suppose it is required to get employee and his manager and hierarchical level of employee in organization. CTE is very useful in such case because of its recursive capability.

Implementation: Let’s understand how it works.

Let’s create table using following script

CREATE TABLE  tbEmployee
(
EmployeeId                INT PRIMARY KEY,
EmployeeName         VARCHAR(50),
ManagerId                 INT
)

Enter some dummy data in table using following insert query:

INSERT tbEmployee 
VALUES 
(25,'Salman',NULL),
(26,'Ranbeer', 25),
(27,'Hrithik',25),
(28,'Aamir',27),
(29,'Shahid',28),
(30,'Sidharth', NULL),
(31,'Varun', 30),
(32,'Kabeer', 30),
(33,'Raj', 29); 

Show table data
SELECT *FROM tbEmployee

Result:
EmployeeId
EmployeeName
ManagerId
25
Salman
NULL
26
Ranbeer
25
27
Hrithik
25
28
Aamir
27
29
Shahid
28
30
Sidharth
NULL
31
Varun
30
32
Kabeer
30
33
Raj
29

CTE recursive query to get employee and manager relationship hierarchy with level.

;WITH EMP_CTE AS
(
SELECT EmployeeId, EmployeeName, ManagerId, CAST('' AS VARCHAR(50)) ManagerName, 0 AS EmployeeLevel FROM tbEmployee WHERE ManagerId IS NULL
UNION ALL
SELECT T.EmployeeId,T.EmployeeName, T.ManagerId,CAST(C.EmployeeName AS VARCHAR(50)) ManagerName, EmployeeLevel + 1 AS EmployeeLevel FROM tbEmployee AS T
INNER JOIN EMP_CTE  AS C ON C.EmployeeId=T.ManagerId
)
SELECT * FROM EMP_CTE

Result:
EmloyeeId
EmployeeName
ManagerId
ManagerName
EmployeeLevel
25
Salman
NULL

0
30
Sidharth
NULL

0
31
Varun
30
Sidharth
1
32
Kabeer
30
Sidharth
1
26
Ranbeer
25
Salman
1
27
Hrithik
25
Salman
1
28
Aamir
27
Hrithik
2
29
Shahid
28
Aamir
3
33
Raj
29
Shahid
4

Explanation: The base record for the CTE is obtained by the first select query above UNION ALL. It gets all EmployeeId which don’t have ManagerId ie. NULL value. This means they are the top most employees of the organization so their Employee Level is set to 0.

Second select query below UNION ALL is executed recursively to get results and it will continue until it returns no rows. E.g. Result will have EmployeeIds which have ManagerId (i.e, EmployeeId of the first result).  This is obtained by joining our CTE result with tbEmployee table on columns EmployeeId of CTE with ManagerId of table tbEmployee. 

This process is recursive and will continue till there is no ManagerId who doesn’t have EmployeeId.

Now over to you:
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