SQL - Assignment in CASE inside a SELECT in a Recursive Query - sql

Question

I'm creating a SQL Server 2008 query that would output the list of employees in a company along with the team they are on with an additional column.
Example of the org tree:
Level 0: CEO
Level 1: A, B, and C
Level 2:
For A:1,2,3
For B:4,5,6
For C:7,8,9
In my resulting set, I should see three columns -- name, level (of the tree), and team. For 1,2, and 3, I'd see 'A' as their team and 2 as the level. For 4,5, and 6, 'B' and 2 for the level and so on.
I'm using a recursive query to navigate the tree (no problems there), but since I need to "carry" the team name down the query (in case there's a level 8 -- it should still show the person in level 1 they report to), I'm doing this:
(...)
UNION ALL
-- Recursive Member Definition
-- in here level increments one each time, and the team should output the child
-- of the top manager
SELECT A.treenodeid, A.parentnodeid, A.email, LEVEL+1, team =
CASE LEVEL
When 1 then SET #salead = A.Email
Else #salead
END
FROM XX as A
INNER JOIN TeamsTable as B on A.parentnodeid = b.treenodeID
Since I'm trying to use a CASE to check if the level is 1 (to update the team name to whatever the team lead's email name is), SQL keeps saying that in the case I have "Incorrect syntax near SET".
Is it possible to do this sort of assignment in a CASE? I've looked around and haven't found if this can work with my recursive case.
Here's all the query (assuming that the root is 'JohnSmith'):
WITH TeamsTable (treenodeid, parentnodeid, email, Level, team)
AS
(
-- Anchor - Level starts with 0, and the team is empty for the top manager
SELECT treenodeid,parentnodeid,email,0,''
FROM XX WHERE email = 'JohnSmith'
UNION ALL
-- Recursive Member Definition - in here level increments one each time, and the team should output the child of the top manager
SELECT
A.treenodeid, A.parentnodeid, A.email, LEVEL+1, team =
CASE LEVEL
When 1 then SET #salead = A.Email
Else #salead
END
FROM XX as A
INNER JOIN TeamsTable as B on A.parentnodeid = b.treenodeID
)
-- Statement that executes the CTE
SELECT *
FROM TeamsTable
Thanks a lot, guys!

Answer 1

Why do you need the variable at all? I don't see it being used subsequently

Answer 2

I would approach this problem from the bottom up, not from the top down.
You've not said what teams A, B, C or CEO should be in, so I've made that up.
I've also included the sample data in a usable form:
create table Org (
ID int not null,
Name varchar(10) not null,
ParentID int null
)
go
insert into Org (ID,Name,ParentID) values
(1,'CEO',null),
(2,'A',1),
(3,'B',1),
(4,'C',1),
(5,'1',2),
(6,'2',2),
(7,'3',2),
(8,'4',3),
(9,'5',3),
(10,'6',3),
(11,'7',4),
(12,'8',4),
(13,'9',4)
Query:
;With AllPeople as (
select ID,ID as LastParentID,ParentID as NextParentID, CASE WHEN ParentID is null THEN 0 ELSE 1 END as Level
from Org
union all
select ap.ID,ap.NextParentID,o.ParentID,Level + 1
from
AllPeople ap
inner join
Org o
on
ap.NextParentID = o.ID and
o.ParentID is not null
), Roots as (
select ID from Org where ParentID is null
), RootedPeople as (
select * from AllPeople where NextParentID is null or NextParentID in (select ID from Roots)
), Names as (
select
oself.Name,
oteam.Name as Team,
Level
from
RootedPeople rp
inner join
Org oself on rp.ID = oself.ID
left join
Org oteam on rp.LastParentID = oteam.ID
)
select * from Names
Result:
Name Team Level
---------- ---------- -----------
CEO CEO 0
A A 1
B B 1
C C 1
9 C 2
8 C 2
7 C 2
6 B 2
5 B 2
4 B 2
3 A 2
2 A 2
1 A 2
Explanation of the CTEs:
AllPeople is a recursive query that climbs up the organisation tree until it reaches the root. We use two columns (LastParentID and NextParentID) to track two levels of the hierarchy - because, apparently, once we reach the root, we want the level before that.
Roots finds all of the people who don't have a parent. It's how we identify the rows from AllPeople that were complete, in,
RootedPeople where we find rows which never successfully found any parents, or where the recursion had reached the top of the tree.
Names and finally we join back to the Org table to assign names to individuals and teams. This one isn't necessary - it could be the final query by itself.
Note also that, due to the recursive way the AllPeople CTE is built, we calculate the levels as we go - every time we recurse, we add one to the Level that this row represents.