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Hierarchical SQL table and finding a record's lineage

Posted on 2010-11-29
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Last Modified: 2012-05-10
Hello.

I have a hierarchical SQL table mimicking a directory tree structure, with fields like the following:

ID
ParentID
ItemName

where a record's ParentID is defined as the ID of the record's intended parent record.

When I preform a Select, I would like to add a column, named "Path", that contains a string representation of an item's lineage, (Eg \GrandParent\Parent\Me).  Given the ID of any item within the table, how do I design a select command to recursively build a lineage string?  I use the word "recursion" loosely -- I know that actual recursion is a resource hog.  Does anyone have a workable strategy for this?

Something like:
SELECT ID, ParentID, ItemName (...something...) as Path
FROM MyTable
WHERE ID=@ID
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Question by:ewolsing
3 Comments
 
LVL 18

Expert Comment

by:lludden
ID: 34231954
If you are using SQL 2005 or later, you might try a recursive CTE as opposed to a recursive function.

Check this MSDN article.

http://msdn.microsoft.com/en-us/library/ms186243.aspx
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Accepted Solution

by:
cyberkiwi earned 2000 total points
ID: 34232256
A sample
create table tree (ID int, ParentID int, ItemName varchar(100))
insert tree select
1,null,'GrandParent' union all select
2,1,'Parent' union all select
3,2,'Me'
GO

create function dbo.lineage(@id int)
returns varchar(max)
as
begin
declare @path varchar(max);
with tmp as (
	select level=1, parentId,convert(varchar(max),'\'+ItemName) Path
	from tree where id=@id
	union all
	select level+1,t.parentID,'\'+t.ItemName+tmp.path
	from tmp
	inner join tree t on tmp.parentID=t.id
	)
select top(1) @path=path from tmp order by level desc
return @path
end
GO

select id, parentid, dbo.lineage(id) as path
from tree
where id=3

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Author Closing Comment

by:ewolsing
ID: 34232734
Thank you!  That was exactly what I was looking for.  While I've done a fair amount of SQL work, I've never played with recursion before.  I appreciate the insight.
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