?
Solved

adjacency model + rec. CTE to determine leaf

Posted on 2009-07-02
6
Medium Priority
?
475 Views
Last Modified: 2012-05-07
I have a table that uses the adjacency approach to model hierarchies:

ItemId      ItemName      ParentId
5      parent1  NULL
6      c2 5
7      c3 6
8      c1 5
9      parent2 NULL
10      c5 9
11      c6 10
12      c4 9

This query determines the level of each node in the tree:

with Hierachy(ItemId, ItemName, ParentId, Level) as
(
      select ItemId, ItemName, ParentId, 0 as Level
      from Items e  
      WHERE ParentID IS NULL
      union all  
      select e.ItemId, e.ItemName, e.ParentId, eh.Level + 1
      from Items e inner join Hierachy eh on e.ParentId = eh.ItemId
)
select ItemId, ItemName, ParentId, Level from Hierachy

I am interested in determining whether a node is a leaf or not. Is there an easy way to do this? Otherwise, I would have to implement a tie-breaker using correlated sub queries ...

Thanks.

Best wishes,

Christian
0
Comment
Question by:csetzkorn
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
  • 2
6 Comments
 
LVL 60

Expert Comment

by:Kevin Cross
ID: 24764327
By leaf, you mean it has no children of its own correct.  If so, then you can tell a leaf if there is not a record that notes its id as a parentid.
SELECT ItemId, ItemName, ParentId
FROM Items i
WHERE NOT EXISTS (
   SELECT 1
   FROM Items p
   WHERE p.ParentId = i.ItemID
);

Open in new window

0
 
LVL 23

Expert Comment

by:Racim BOUDJAKDJI
ID: 24764412
<<I am interested in determining whether a node is a leaf or not. Is there an easy way to do this?>>
A more correct and simple to maintain way to represent hierarchies in relational perspective is the following.

item
name        
----------
parent1        
c2                
c3                
c1                
parent2        
c4                                
c5                
c6                

item_lineage
parent          child
-----------------------
parent1         c1
parent1         c2
c2                 c3
parent2         c5
parent2         c4
c5                 c6


<<I am interested in determining whether a node is a leaf or not.>>
With above design:

> you can test whether an item is a leaf simply by using the exists function

if exists(select 1 from lineage where child = 'identifier of the leaf')

> you *can* have many parent for the same child
> you can actually (if you want to) have a specific item belong to several hierarchies at different level of depth.
you can determine the level of a node simply by running


declare @counter int, @item varchar(30)
set @counter = 0
set @item = 'c6'
while exist(select 1 from lineage where child = @item )
begin
         set @counter = @counter + 1
         select @item = parent from lineage where child = @item
end

returns 2...

Hope this helps...
0
 

Author Comment

by:csetzkorn
ID: 24764440
Thanks. That makes sense. This is what I have so far:

with Hierachy(ItemId, ItemName, ParentId, Level) as
(
      select ItemId, ItemName, ParentId, 0 as Level
      from Items e  
      WHERE ParentID IS NULL
      union all  
      select e.ItemId, e.ItemName, e.ParentId, eh.Level + 1
      from Items e inner join Hierachy eh on e.ParentId = eh.ItemId
)
select
ItemId,
ItemName,
ParentId,
Level,
case when (select count(*) from Items as i where h.itemid = i.parentid) > 0 then 'false' else 'true' end as isLeaf
from Hierachy as h
order by itemid

is there anything that can be optimised?

C
0
Get proactive database performance tuning online

At Percona’s web store you can order full Percona Database Performance Audit in minutes. Find out the health of your database, and how to improve it. Pay online with a credit card. Improve your database performance now!

 

Author Comment

by:csetzkorn
ID: 24764457
Racimo,

Thanks. I am usually also using nested set approach. Would have to investigate how to get this done using NHibernate. But thanks anyway.

C
0
 
LVL 23

Expert Comment

by:Racim BOUDJAKDJI
ID: 24764553
<<Thanks. I am usually also using nested set approach. Would have to investigate how to get this done using NHibernate. But thanks anyway.>>
This should not be an issue since Hibernate is only a query formulator.  And since you already know this approach,  I suggest you consider forgetting the other.   You noticed how this *adjacency* approach makes things more complex to establish even the simplest information.  Alternatively, the other way makes it (almost) a child's game.  

Anyway good luck...
0
 
LVL 60

Accepted Solution

by:
Kevin Cross earned 2000 total points
ID: 24764681
Looks fine.  For large data sets, you can consider casting as BIT so that returned data is smaller footprint.

cast(case when (select count(*) from Items as i where h.itemid = i.parentid) > 0 then 0 else1 end as BIT) as isLeaf
0

Featured Post

Optimize your web performance

What's in the eBook?
- Full list of reasons for poor performance
- Ultimate measures to speed things up
- Primary web monitoring types
- KPIs you should be monitoring in order to increase your ROI

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

In part one, we reviewed the prerequisites required for installing SQL Server vNext. In this part we will explore how to install Microsoft's SQL Server on Ubuntu 16.04.
It is possible to export the data of a SQL Table in SSMS and generate INSERT statements. It's neatly tucked away in the generate scripts option of a database.
Viewers will learn how to use the SELECT statement in SQL and will be exposed to the many uses the SELECT statement has.
Viewers will learn how to use the UPDATE and DELETE statements to change or remove existing data from their tables. Make a table: Update a specific column given a specific row using the UPDATE statement: Remove a set of values using the DELETE s…
Suggested Courses

752 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question