What is the simplest way of doing a recursive self-join in SQL Server? I have a table like this:
PersonID | Initials | ParentID
1 CJ NULL
2 EB 1
3 MB 1
4 SW 2
5 YT NULL
6 IS 5
And I want to be able to get the records only related to a hierarchy starting with a specific person. So If I requested CJ's hierarchy by PersonID=1 I would get:
PersonID | Initials | ParentID
1 CJ NULL
2 EB 1
3 MB 1
4 SW 2
And for EB's I'd get:
PersonID | Initials | ParentID
2 EB 1
4 SW 2
I'm a bit stuck on this can can't think how to do it apart from a fixed-depth response based on a bunch of joins. This would do as it happens because we won't have many levels but I would like to do it properly.
Thanks! Chris.
WITH q AS
(
SELECT *
FROM mytable
WHERE ParentID IS NULL -- this condition defines the ultimate ancestors in your chain, change it as appropriate
UNION ALL
SELECT m.*
FROM mytable m
JOIN q
ON m.parentID = q.PersonID
)
SELECT *
FROM q
By adding the ordering condition, you can preserve the tree order:
WITH q AS
(
SELECT m.*, CAST(ROW_NUMBER() OVER (ORDER BY m.PersonId) AS VARCHAR(MAX)) COLLATE Latin1_General_BIN AS bc
FROM mytable m
WHERE ParentID IS NULL
UNION ALL
SELECT m.*, q.bc + '.' + CAST(ROW_NUMBER() OVER (PARTITION BY m.ParentID ORDER BY m.PersonID) AS VARCHAR(MAX)) COLLATE Latin1_General_BIN
FROM mytable m
JOIN q
ON m.parentID = q.PersonID
)
SELECT *
FROM q
ORDER BY
bc
By changing the ORDER BY
condition you can change the ordering of the siblings.