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

I need to find a solution for the same task, found some articles, but still didn't choose which way to go...

http://explainextended.com/2009/07/20/hierarchical-data-in-mysql-parents-and-children-in-one-query/

May be these links might help you. If you find a good solution - please post it here. i'm not allowed to post more then 1 link - i will add some to next posts

Answer 2

Oracle has a very convenient syntax for retrieving hierarchical data like this:

select
    item_id,
    item_parent,
    level as depth
from
    items
connect by
    prior item_id = item_parent
start with
    item_parent not in (select item_id from items)

This starts with the root nodes of your trees as those items whose item_parent does not exist in the table as item_id, and selects all children of those nodes, along with their depth in the tree.

Answer 3

There is a good tech article on the mysql website about hierarchical data in MySql: Managing Hierarchical Data in MySQL - you can find a few detailed solutions with pro and cons there.

Especially the part about "The Nested Set Model" and "Finding the Depth of the Nodes" should be of interest for you.

Answer 4

MySQL

• http://www.artfulsoftware.com/mysqlbook/sampler/mysqled1ch20.html
• http://mikehillyer.com/articles/managing-hierarchical-data-in-mysql/

EDIT: removed unnecessary information

Answer 5

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.