SQL recursive udf always returns null - sql

Question

Create Table Employees
(
Employee varchar(10),
Manager varchar(10)
);
Insert into Employees
values
('Charlie',null),
('Peter','James'),
('Elai',null),
('Graham','Emanuel'),
('Amanda','Charlie'),
('Sen','Graham'),
('Emanuel',null),
('James','Amanda'),
('Elai',null),
('Victor','Elai');
Above "Employees" table contains employee and employee's manager name. When trying to retrieve comma separated hierarchy of a employee using below function, the result is always null.
for example :
employee 'Victor', hierarchy/result should be "Victor, Elai".
Could anyone point out what am I doing wrong in below UDF.
Create Function EmployeeHierarchy(#employeeName varchar(20))
Returns varchar(100)
AS
Begin
Declare #commaSeparatedHierarchy varchar(100);
Declare #manager varchar(20);
if(#employeeName is not null)
Begin
Select #manager=Manager from Employees where Employee=#employeeName;
Set #commaSeparatedHierarchy=dbo.EmployeeHierarchy(#manager)+','+#manager;
End
return #commaSeparatedHierarchy;
End;

Answer 1

First & foremost, you DO NOT want to create this as a scalar function. Their performance is horrible any udf you create, should be created as an inline table valued function. The following should do what you're looking for...
-- the test data...
USE tempdb;
GO
IF OBJECT_ID('tempdb.dbo.Employee', 'U') IS NOT NULL
DROP TABLE dbo.Employee;
CREATE TABLE dbo.Employee (
Employee varchar(10),
Manager varchar(10)
);
INSERT dbo.Employee (Employee, Manager) VALUES
('Charlie',null),
('Peter','James'),
('Elai',null),
('Graham','Emanuel'),
('Amanda','Charlie'),
('Sen','Graham'),
('Emanuel',null),
('James','Amanda'),
('Elai',null),
('Victor','Elai');
SELECT * FROM dbo.Employee e;
iTVF code...
CREATE FUNCTION dbo.EmployeeHierarchy
(
#employeeName varchar(20)
)
RETURNS TABLE WITH SCHEMABINDING AS
RETURN
WITH
cte_Recur AS (
SELECT
CSH = CAST(CONCAT(e.Employee, ', ' + e.Manager) AS VARCHAR(1000)),
e.Manager,
NodeLevel = 1
FROM
dbo.Employee e
WHERE
e.Employee = #employeeName
UNION ALL
SELECT
CSH = CAST(CONCAT(r.CSH, ', ' + e.Manager) AS VARCHAR(1000)),
e.Manager,
NodeLevel = r.NodeLevel + 1
FROM
dbo.Employee e
JOIN cte_Recur r
ON e.Employee = r.Manager
WHERE
e.Manager IS NOT NULL
)
SELECT
commaSeparatedHierarchy = MAX(r.CSH)
FROM
cte_Recur r;
GO
Sample execution...
SELECT
eh.commaSeparatedHierarchy
FROM
dbo.EmployeeHierarchy('peter') eh;
... and the results...
commaSeparatedHierarchy
------------------------------
Peter, James, Amanda, Charlie