Getting hierarchy data from self-referencing tables

Question

Let\'s say you have the following table:

items(item_id, item_parent)  

... and it is a self-referencing table - item_parent r

Answer 1

If the database is SQL 2005 / 2008 then...

The easiest way to get this is using a CTE (Common Table Expression) that is designed to recurse.

 WITH myCTE (Item_id, Depth)
 AS
 (
    Select Item_ID, 0 as Depth From yourTable where Item_Parent=0
    Union ALL
    Select yourTable.Item_ID, Depth + 1 
    From yourTable 
    inner join myCte on yourTable.item_Parent = myCte.Item_Id
 )

 Select Item_id, Depth from myCTE

The output is as follows:

Item_Id  Depth
    1   0
    2   0
    3   1
    4   1
    5   2

From that you can format it as you wish.