SQL Server - Self Join - sql

Question

I have a table as follows
EmployeeID Name ManagerID
2 David 3
3 Roger NULL
4 Marry 2
5 Joseph 2
7 Ben 2
Here Roger is Top Manager
Mike & David are Managers
And rest all are employees
I am looking for output like this:
EmployeeName ManagerName TopManager
Marry David Roger
Joseph David Roger
Ben David Roger
NULL David Roger
I tried using Self Join like:
SELECT e1.Name EmployeeName, ISNULL(e2.name, 'Top Manager') AS ManagerName
FROM Employee e1
LEFT JOIN Employee e2
ON e1.ManagerID = e2.EmployeeID
but it is not giving the output I am looking for.

Answer 1

If you can have different top managers, then a recursive CTE is needed:
with cte as (
select employeeid, name, name as topmanager
from Employee
where managerid is null
union all
select t.employeeid, t.name, cte.topmanager
from Employee t join
cte
on t.managerid = cte.employeeid
)
select *
from cte;
If there is only one top manager, then:
select e.*, topm.name as topmanager
from employee e cross join
(select e2.* from employee e2 where e2.managerid is null) as topm

Answer 2

I think you have to do self join twice to get the desired output.
I created the query in this way and got the output which you have mentioned. Please note that I did not include the last row which has null value, and rest the same as it is.
Query:
create table Employees (EmployeeID int, Name varchar(10), ManagerID int)
Insert into Employees values
(2, 'David' , 3 )
,(3, 'Roger' , NULL)
,(4, 'Marry' , 2 )
,(5, 'Joseph' , 2 )
,(7, 'Ben' , 2 )
select e.name as EmployeeName, e1.name ManagerName, e2.Name TopManager
from Employees e
left join Employees e1 on e.ManagerID = e1.employeeid
left join Employees e2 on e1.ManagerID = e2.EmployeeID
where e.ManagerID is not null and e1.ManagerID is not null
Where condition was given to restrict the manager names in Employee column.
Output:
EmployeeName ManagerName TopManager
Marry David Roger
Joseph David Roger
Ben David Roger