SQL: Optimizing Recursive CTE - sql

Question

Example table structure:
EmployeeId TeamleaderId TopTeamleaderId LEVEL ParentTree CompanyId
1 0 0 0 NULL 1
2 1 1 1 2>1 1
3 2 1 2 3>2>1 1
TeamleaderId is foreignKey reference to EmployeeId in the same table
Goal:
Whenever a row is inserted in the table with EmployeeId, TeamleaderId, CompanyId automatically populate TopTeamleaderId, LEVEL and ParentTree with AFTER INSERT trigger
Code:
WITH CTE AS (
SELECT EmployeeId, TeamleaderId,0 AS [Level], CAST(EmployeeId AS varchar(100)) AS Heirarchy, TopTeamleaderId
FROM dbo.Employee
WHERE EmployeeId IN (SELECT EmployeeId FROM Employee WHERE TeamleaderId IS NULL
AND CompanyId IN(SELECT DISTINCT CompanyId FROM INSERTED))
UNION ALL
SELECT mgr.EmployeeId, mgr.TeamleaderId, CTE.[Level] +1 AS [Level],
CAST(( CAST(mgr.EmployeeId AS VARCHAR(100)) + '>' + CTE.Heirarchy) AS varchar(100)) AS Heirarchy, CTE.TopTeamleaderId
FROM CTE
INNER JOIN dbo.Employee AS mgr
ON TaskCTE.EmployeeId = mgr.ParentTeamleaderId
)
UPDATE Employee SET [LEVEL] = TC.[LEVEL], ParentTree = TC.Heirarchy, TopTeamleaderId = TC.TopTeamleaderId
FROM dbo.Employee AS Employee
JOIN (SELECT * FROM CTE WHERE EmployeeId IN(SELECT DISTINCT EmployeeId FROM INSERTED) AND ParentTeamleaderId IS NOT NULL) TC
ON
Employee.EmployeeId = TC.EmployeeId
Problem:
Imagine there are like 1000000 employees in a company, this query would take a long time to execute. How to optimize it so that only the parents of the inserted row are taken in to account?

Answer 1

Recursive CTE's are great, but as you can see the perfomance can suffer with larger hierarchies. It is my firm belief that there is no shame in temp tables.
The following will generate a 200K point hierarchy in 0.784 seconds.
Example
Select EmployeeId
,TeamleaderId
,Lvl=1
,TopTeamleaderId = 0
,ParentTree=cast(EmployeeId as varchar(500))
,CompanyID
Into #TempBld
From Employee
Where TeamleaderId is null
Declare #Cnt int=1
While #Cnt<=30 --<< Set Your Max Level
Begin
Insert Into #TempBld
Select A.EmployeeId
,A.TeamleaderId
,B.Lvl+1
,IIF(B.Lvl=1,B.EmployeeId,B.TopTeamleaderId)
,concat(A.EmployeeId,'>',B.ParentTree)
,A.CompanyID
From Employee A
Join #TempBld B on (B.Lvl=#Cnt and A.TeamleaderId=B.EmployeeId)
Set #Cnt=#Cnt+1
End
--Select * from #TempBld Order by ParentTree
Returns