Here's one way of doing it; it uses a recursive CTE to find the ancestry of a node, and uses "CROSS APPLY" over the input values to get the common ancestry; you just change the values in @ids
(table variable):
----------------------------------------- SETUP
CREATE TABLE MyData (
Id int NOT NULL,
ParentId int NULL)
INSERT MyData VALUES (1,NULL)
INSERT MyData VALUES (2,1)
INSERT MyData VALUES (3,1)
INSERT MyData VALUES (4,2)
INSERT MyData VALUES (5,2)
INSERT MyData VALUES (6,3)
INSERT MyData VALUES (7,3)
INSERT MyData VALUES (8,7)
GO
CREATE FUNCTION AncestorsUdf (@Id int)
RETURNS TABLE
AS
RETURN (
WITH Ancestors (Id, ParentId)
AS (
SELECT Id, ParentId
FROM MyData
WHERE Id = @Id
UNION ALL
SELECT md.Id, md.ParentId
FROM MyData md
INNER JOIN Ancestors a
ON md.Id = a.ParentId
)
SELECT Id FROM Ancestors
);
GO
----------------------------------------- ACTUAL QUERY
DECLARE @ids TABLE (Id int NOT NULL)
DECLARE @Count int
-- your data (perhaps via a "split" udf)
INSERT @ids VALUES (6)
INSERT @ids VALUES (7)
INSERT @ids VALUES (8)
SELECT @Count = COUNT(1) FROM @ids
;
SELECT TOP 1 a.Id
FROM @ids
CROSS APPLY AncestorsUdf(Id) AS a
GROUP BY a.Id
HAVING COUNT(1) = @Count
ORDER BY a.ID DESC
Update if the nodes aren't strictly ascending:
CREATE FUNCTION AncestorsUdf (@Id int)
RETURNS @result TABLE (Id int, [Level] int)
AS
BEGIN
WITH Ancestors (Id, ParentId, RelLevel)
AS (
SELECT Id, ParentId, 0
FROM MyData
WHERE Id = @Id
UNION ALL
SELECT md.Id, md.ParentId, a.RelLevel - 1
FROM MyData md
INNER JOIN Ancestors a
ON md.Id = a.ParentId
)
INSERT @result
SELECT Id, RelLevel FROM Ancestors
DECLARE @Min int
SELECT @Min = MIN([Level]) FROM @result
UPDATE @result SET [Level] = [Level] - @Min
RETURN
END
GO
and
SELECT TOP 1 a.Id
FROM @ids
CROSS APPLY AncestorsUdf(Id) AS a
GROUP BY a.Id, a.[Level]
HAVING COUNT(1) = @Count
ORDER BY a.[Level] DESC