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recursive query
Posted on 2011-03-09
How does one write a recursive query? This would come into play where a table is self-referencing. Like, a list of employees, where there is a primary Key and supervisor column, where the latter maps to the primary key. So, If I want a list of employees everyone from person "X" on down, how do I do this?
[X]
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4 Comments
here is an example
ID Parent
1 null
2 1
3 1
4 null
5 4
6 5
with CTE(ID, PARENT)
AS
(
SELECT F.ID, F.PARENT
FROM TABLE1 F
WHERE PARENT IS NULL
UNION ALL
SELECT F.ID, F.PARENT
FROM TABLE1 F
INNER JOIN CTE FH ON FH.ID = F.PARENT
)
SELECT ID, PARENT FROM CTE
ID Parent
1 null
2 1
3 1
4 null
5 4
6 5
with CTE(ID, PARENT)
AS
(
SELECT F.ID, F.PARENT
FROM TABLE1 F
WHERE PARENT IS NULL
UNION ALL
SELECT F.ID, F.PARENT
FROM TABLE1 F
INNER JOIN CTE FH ON FH.ID = F.PARENT
)
SELECT ID, PARENT FROM CTE
I believe you are looking to make a tree for employee:
See example below:
ID: Emp ID
Name: Emp Name
Manager: Emp. Manager ID (NULL: Emp. have no manager)
ID Name Manager
1 a NULL
2 b 1
3 c 1
4 X 2
5 Y 2
6 Z 1
7 P 3
See example below:
ID: Emp ID
Name: Emp Name
Manager: Emp. Manager ID (NULL: Emp. have no manager)
ID Name Manager
1 a NULL
2 b 1
3 c 1
4 X 2
5 Y 2
6 Z 1
7 P 3
WITH Employee_Tree (ID,
Name,
Manager,
Depth) AS(
SELECT ID,
Name,
Manager,
1 AS depth
FROM Employee WITH (NOLOCK)
WHERE MANAGER IS NULL
UNION ALL
SELECT N.ID,
N.Name,
N.Manager,
ET.Depth + 1
FROM Employee AS N WITH (NOLOCK)
INNER JOIN Employee_Tree ET
ON ET.ID = N.Manager)
SELECT ID,
Name,
Manager,
FROM Employee_Tree
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