Limiting recursion to certain level - sql

Question

I have a SQL table named Player and another called Team.
Each Player MUST belong to a team via a foreign key TeamID.
Each Team can belong to another Team via a recursive field ParentTeamID.
So it could be (top down)...
TeamA
TeamB
Team76
Group8
Player_ME
My question is, if I'm given a Player's PlayerID (the PK for that table), what is the best way to get the top Team?
My query so far (which gets all teams):
WITH TeamTree
AS (
SELECT ParentTeam.*, Player.PlayerID, 0 as Level
FROM Team ParentTeam
INNER JOIN Player ON Player.TeamID = ParentTeam.TeamID
WHERE Player.PlayerID IN (SELECT * FROM dbo.Split(#PlayerIDs,','))
UNION ALL
SELECT ChildTeam.*, TeamTree.PlayerID AS PlayerID, TeamTree.Level + 1
FROM Team ChildTeam
INNER JOIN TeamTree TeamTree
ON ChildTeam.TeamID = TeamTree.ParentTeamID
)
Now whilst I think this is the right place to start I think there may be a better way. Plus I'm kinda stuck! I tried using Level in a join (inside a subquery) but it didn't work.
Any ideas on how to work my way up the tree and get only the top level details?
Edit:
A ParentTeam CAN be a ParentTeam (infinite recursion), but a Player can only belong to one Team.
Data Structure
Team:
TeamID (PK), Name, ParentTeamID (Recursive field)
Player:
PlayerID (PK), Name, TeamID (FK)
Sample Data:
Team:
1, TeamA, NULL
2, TeamB, 1
3, Team76, 2
4, Group8, 3
Player:
1, Player_ME, 4
2, Player_TWO, 2
So with the above data, both players should show (in the query) that they have a "TopLevelTeam" of TeamA

Answer 1

I believe this is what you are looking for, with a bit of extra info thrown in for free :-)
Andrew had the correct idea in his edited version, but I think his implementation is incorrect.
The schema and query are available at SQL Fiddle
with teamCTE as (
select TeamID,
TeamName,
cast(null as int) as ParentTeamID,
cast(null as varchar(10)) as ParentTeamName,
TeamID TopTeamID,
TeamName TopTeamName,
1 as TeamLevel
from team
where ParentTeamID is null
union all
select t.TeamID,
t.TeamName,
c.TeamID,
c.TeamName,
c.TopTeamID,
c.TopTeamName,
TeamLevel+1 as TeamLevel
from team t
join teamCTE c
on t.ParentTeamID = c.TeamID
)
select p.PlayerID,
p.PlayerName,
t.*
from player p
join teamCTE t
on p.TeamID = t.TeamID
EDIT - answer to question in comment
You can navigate to any level within the player's team hierarchy simply by joining to the CTE a 2nd time. In your case you asked for the 2nd top most team: SQL Fiddle
with teamCTE as (
select TeamID,
TeamName,
cast(null as int) as ParentTeamID,
cast(null as varchar(10)) as ParentTeamName,
TeamID TopTeamID,
TeamName TopTeamName,
1 as TeamLevel
from team
where ParentTeamID is null
union all
select t.TeamID,
t.TeamName,
c.TeamID,
c.TeamName,
c.TopTeamID,
c.TopTeamName,
TeamLevel+1 as TeamLevel
from team t
join teamCTE c
on t.ParentTeamID = c.TeamID
)
select p.PlayerID,
p.PlayerName,
t1.*,
t2.TeamID Level2TeamID,
t2.TeamName Level2TeamName
from player p
join teamCTE t1
on p.TeamID = t1.TeamID
join teamCTE t2
on t1.TopTeamID = t2.TopTeamID
and t2.TeamLevel=2

Answer 2

WITH TeamTree
AS (
SELECT ParentTeam.*, Player.PlayerID AS UrPlayerID, 0 as Level
FROM Team ParentTeam
INNER JOIN Player ON Player.TeamID = ParentTeam.TeamID
WHERE Player.PlayerID IN (SELECT * FROM dbo.Split(#PlayerIDs,','))
UNION ALL
SELECT ChildTeam.*, TeamTree.PlayerID AS PlayerID, TeamTree.Level + 1
FROM Team ChildTeam
INNER JOIN TeamTree TeamTree
ON ChildTeam.ParentTeamID = TeamTree.TeamID /* These were reversed, I think */
AND UrPlayerID=ChildTeam.PlayerID /* ADDED */
)
Otherwise you get a huge duplication of rows, something like the square of the number of players, don't you?
--
(After comment below)
Quite right, I misread the schema. Look, you don't need to bring the player in until the very end. I thought the team tree arrangement might differ by player, but it doesn't. So
WITH recursive TeamTree AS (
SELECT TeamID, ParentTeamID FROM Team T1
UNION ALL
SELECT T1.TeamID, T2.ParentTeamID FROM T1 JOIN T2 ON T1.ParentTeamID=T2.TeamID
)
SELECT TeamTree.* FROM TeamTree JOIN Team T3
ON TeamTree.ParentTeamID=T3.TeamID WHERE T3.ParentTeamID IS NULL;
This gives you a table of each team and its root ancestor. Now join that to the player table.
SELECT * FROM Player JOIN (WITH TeamTree AS (
SELECT TeamID, ParentTeamID FROM Team T1
UNION ALL
SELECT T1.TeamID, T2.ParentTeamID FROM T1 JOIN T2 ON T1.ParentTeamID=T2.TeamID
)
SELECT TeamTree.* FROM TeamTree JOIN Team T3
ON TeamTree.ParentTeamID=T3.TeamID WHERE T3.ParentTeamID IS NULL) teamtree2
ON Player.TeamID=teamtree2.TeamID;
You can rejoin with Team if you need more columns.