SQL Server parent child (parent see all everything)? - sql-server

Question

This is my table:
EmployeeID Employee ManagerID
---------------------------------
1 Anna 5
2 John 4
3 Steve 4
4 Lisa 1
5 Adam NULL
6 Per 1
There is no problem for me to get parent and child relationship with a self-join like this:
SELECT
E.EmployeeID,
E.Employee AS Employee,
E.ManagerID,
M.Employee AS Manager
FROM
Employee AS E
LEFT JOIN
Employee AS M ON E.ManagerID = M.EmployeeID
EmployeeID Employee ManagerID Manager
1 Anna 5 Adam
2 John 4 Lisa
3 Steve 4 Lisa
4 Lisa 1 Anna
5 Adam NULL NULL
6 Per 1 Anna
However, How would i go about to make sure that the parent see the whole hierarchy level?
I would like the table to look like this:
EmployeeID Manager Employee EmployeeID
5 Adam Anna 1
5 Adam Per 6
5 Adam Lisa 4
5 Adam John 2
5 Adam Steve 3
1 Anna Per 6
1 Anna Lisa 4
1 Anna John 2
1 Anna Steve 3
4 Lisa John 2
4 Lisa Steve 3
Note: in this example i only have 3 levels of manger but there can be many more

Answer 1

You can try this:
DECLARE #DataSource TABLE
(
[EmployeeID] TINYINT
,[Employee] VARCHAR(12)
,[ManagerID] TINYINT
);
INSERT INTO #DataSource ([EmployeeID], [Employee], [ManagerID])
VALUES (1, 'Anna', 5)
,(2, 'John', 4)
,(3, 'Steve', 4)
,(4, 'Lisa', 1)
,(5, 'Adam', NULL)
,(6, 'Per', 1);
WITH DataSource AS
(
SELECT DISTINCT DS1.*
,0 AS [Level]
,DS1.[EmployeeID] AS Parent
FROM #DataSource DS1
INNER JOIN #DataSource DS2
ON DS1.[EmployeeID] = DS2.[ManagerID]
UNION ALL
SELECT DS2.*
,DS1.[Level] + 1
,DS1.Parent
FROM DataSource DS1
INNER JOIN #DataSource DS2
ON DS1.[EmployeeID] = DS2.[ManagerID]
)
SELECT DS1.[EmployeeID]
,DS1.[Employee] AS [Manager]
,DS.[EmployeeID]
,DS.[Employee]
FROM DataSource DS
INNER JOIN #DataSource DS1
ON DS.[Parent] = DS1.[EmployeeID]
WHERE DS.[Level] <> 0
ORDER BY DS.[Parent] DESC;
We are using recursive CTE and it may look a kind of messy and complicated if you are seeing this syntax for the first time, but it's nothing special.
When are using recursive CTE run some performance tests in order to be sure it is the right technique for solving your issue.

Answer 2

You should use recursive CTE syntax. In the first iteration (before UNION ALL) you get all Parent-Child pairs. In the recursive part (after UNION ALL) you get the next level child for each pair and substitute it into the pair Parent-Child instead of the Child leaving Parent the same.
WITH CTE AS
(
SELECT TP.EmployeeID as ManagerId,
TP.Employee as Manager,
TC.EmployeeID as EmployeeID,
TC.Employee as Employee
FROM TEmployee as TP
JOIN TEmployee as TC on (TP.EmployeeID = TC.ManagerID)
UNION ALL
SELECT TP.ManagerId as ManagerId,
TP.Manager as Manager,
TC.EmployeeID as EmployeeID,
TC.Employee as Employee
FROM CTE as TP
JOIN TEmployee as TC on (TP.EmployeeID = TC.ManagerID)
)
SELECT * FROM CTE Order By ManagerID
result:
+-----------+---------+------------+----------+
| ManagerId | Manager | EmployeeID | Employee |
+-----------+---------+------------+----------+
| 1 | Anna | 4 | Lisa |
| 1 | Anna | 6 | Per |
| 1 | Anna | 2 | John |
| 1 | Anna | 3 | Steve |
| 4 | Lisa | 2 | John |
| 4 | Lisa | 3 | Steve |
| 5 | Adam | 1 | Anna |
| 5 | Adam | 4 | Lisa |
| 5 | Adam | 6 | Per |
| 5 | Adam | 2 | John |
| 5 | Adam | 3 | Steve |
+-----------+---------+------------+----------+