Given a table with a hierarchyid
type column, how do you write a query to return all rows that are ancestors of a specific node?
There is an IsDescendantOf()
function, which is perfect for getting the children, but there's no corresponding IsAncestorOf()
function to return ancestors (and the absence of a GetAncestors()
function seems like quite an oversight.)
The most commonly used approach would be a recursive Common Table Expression (CTE)
WITH Ancestors(Id, [Name], AncestorId) AS
(
SELECT
Id, [Name], Id.GetAncestor(1)
FROM
dbo.HierarchyTable
WHERE
Name = 'Joe Blow' -- or whatever you need to select that node
UNION ALL
SELECT
ht.Id, ht.[Name], ht.Id.GetAncestor(1)
FROM
dbo.HierarchyTable ht
INNER JOIN
Ancestors a ON ht.Id = a.AncestorId
)
SELECT *, Id.ToString() FROM Ancestors
(adapted from a Simon Ince blog post)
Simon Ince also proposes a second approach where he just basically reverses the condition - instead of detecting those person entries that are an ancestor of the target person, he turns the check around:
DECLARE @person hierarchyid
SELECT @person = Id
FROM dbo.HierachyTable
WHERE [Name] = 'Joe Blow';
SELECT
Id, Id.ToString() AS [Path],
Id.GetLevel() AS [Level],
Id.GetAncestor(1),
Name
FROM
dbo.HierarchyTable
WHERE
@person.IsDescendantOf(Id) = 1
This will select all the rows from your table, where the target person you're interested in is a descendant of - any level down the hierarchy. So this will find that target person's immediate and non-immediate ancestors all the way up to the root.