Update Manager Table Tree by Recursion - tsql

Question

I have a table (see image) Employees (manager is manager of another and so on) with id, parentid, salary, totalsalary. The last one needs to be updated so that every employee had Sum of its Descendants salary. I have already written script, which gets total salary by id and than updates column in cursor, but it's heavy... any other ways?
DECLARE #id INT ;
DECLARE #s INT ;
DECLARE curs CURSOR FOR
SELECT personid FROM dbo.Employees
OPEN curs ;
FETCH NEXT FROM curs INTO #id ;
WHILE ##FETCH_STATUS = 0
BEGIN
WITH Xemps ( ID )
AS ( SELECT PersonID AS ID
FROM dbo.Employees
WHERE PersonID = #id
UNION ALL
SELECT e.PersonID AS ID
FROM dbo.Employees AS e
INNER JOIN Xemps AS x ON e.ManagerID = x.ID
)
SELECT #s = SUM(Salary)
FROM dbo.Employees
WHERE PersonID IN ( SELECT id
FROM Xemps )
UPDATE dbo.Employees
SET SalarySum = #s
WHERE PersonID = #id
FETCH NEXT FROM curs INTO #id
END
CLOSE curs ;
DEALLOCATE curs ;

Answer 1

The cursor is not necessary, this can be done using just a recursive common table expression:
WITH Emp AS
( SELECT EmployeeID, Salary, ManagerID
FROM dbo.Employee
UNION ALL
SELECT e.EmployeeID, e.Salary, Emp.ManagerID
FROM dbo.Employee e
INNER JOIN Emp
ON e.ManagerID = Emp.EmployeeID
)
UPDATE dbo.Employee
SET SalarySum = COALESCE(s.Salary, 0) + e.Salary
FROM dbo.Employee e
LEFT JOIN
( SELECT ManagerID, SUM(Salary) [Salary]
FROM Emp
GROUP BY ManagerID
) s
ON s.ManagerID = e.EmployeeID

Answer 2

Create a function that performs the sum for each employee where they are a manager:
create function dbo.fn_TotalSalary
{
#EmployeeId int
}
returns float
as
begin
declare #totalSalary float
select #totalSalary = sum(salary)
from dbo.employees
where employeeid = #employeeid or managerid = #employeeid
return #totalSalary
end
Then alter the Employees table, changing the TotalSalary column to a computed column using the function:
dbo.fn_TotalSalary(EmployeeId)
As employees earn more, the computed column will update automatically. Then you can simply call
select * from Employees
to get the details. Doing it this way would mean that your data is always 100% accurate and up to date rather than potentially retrieving stale data.