SQL Server CTE Bottom to Top Recursive with Where clause
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22-01-2021 - |
Question
I have an Employee Table with an EmployeeId, ManagerId and a Name field.
The goal is to make a recursive With fetching all the rows from an employee to the top manager (ManagerId is null).
I found this link which helped to get the base of the code but I do not manage to make it work for my case
DECLARE @EmployeeTable table ([EmployeeId] int, [name] varchar(10), [managerId] int)
INSERT @EmployeeTable VALUES (1,'Jerome', NULL ) -- tree is as follows:
INSERT @EmployeeTable VALUES (2,'Joe' ,1) -- 1-Jerome
INSERT @EmployeeTable VALUES (3,'Paul' ,2) -- / \
INSERT @EmployeeTable VALUES (4,'Jack' ,3) -- 2-Joe 9-Bill
INSERT @EmployeeTable VALUES (5,'Daniel',3) -- / \ \
INSERT @EmployeeTable VALUES (6,'David' ,2) -- 3-Paul 6-David 10-Sam
INSERT @EmployeeTable VALUES (7,'Ian' ,6) -- / \ / \
INSERT @EmployeeTable VALUES (8,'Helen' ,6) -- 4-Jack 5-Daniel 7-Ian 8-Helen
INSERT @EmployeeTable VALUES (9,'Bill ' ,1) --
INSERT @EmployeeTable VALUES (10,'Sam' ,9) --
DECLARE @employeeId int = 3
;WITH StaffTree AS
(
SELECT
c.[EmployeeId], c.[name], c.managerId, 0 AS [Level]
FROM @EmployeeTable c
LEFT OUTER JOIN @EmployeeTable cc ON c.managerId=cc.EmployeeId
WHERE c.EmployeeId=@employeeId OR (@employeeId IS NULL AND c.managerId IS NULL)
UNION ALL
SELECT
s.[EmployeeId], s.[name], s.managerId, t.[Level]+1
FROM StaffTree t
INNER JOIN @EmployeeTable s ON t.[EmployeeId]=s.managerId
WHERE s.managerId=@employeeId OR @employeeId IS NULL OR t.Level>1
)
SELECT * FROM StaffTree
In case you select the employee 3 hierarchy, the result should be:
EmployeeId | Name | ManagerId
1 | Jerome | NULL
2 | Joe | 1
3 | Paul | 2
La solution
Swapping the columns in the inner join in the recursive part is a way to go about this.
Join columns changed from t.[EmployeeId]=s.managerId
to s.[EmployeeId]=t.managerId
I deleted some parts that did not seem like they were needed.
DECLARE @employeeId int = 3
;WITH StaffTree AS
(
SELECT
c.[EmployeeId], c.[name], c.managerId, 0 AS [Level]
FROM @EmployeeTable c
WHERE c.EmployeeId=@employeeId OR (@employeeId IS NULL AND c.managerId IS NULL)
UNION ALL
SELECT
s.[EmployeeId], s.[name], s.managerId, t.[Level]+1
FROM StaffTree t
INNER JOIN @EmployeeTable s ON s.[EmployeeId]=t.managerId
)
SELECT EmployeeId,
name,
managerId
FROM StaffTree
ORDER BY managerId asc;
Result
EmployeeId name managerId
1 Jerome NULL
2 Joe 1
3 Paul 2
Autres conseils
It looks like you had a tiny error when copying the example that you linked to -
c.[EmployeeId], c.[name], c.managerId, 0 AS [Level]
should be
c.[EmployeeId], c.[name], c.managerId, 1 AS [Level]
Once I make that change, your code functions the same way as the example.
This Link will help you a lot in learning Recursive CTEs with excellent and useful examples : https://www.codeproject.com/Articles/818694/SQL-queries-to-manage-hierarchical-or-parent-child.