List:General Discussion« Previous MessageNext Message »
From:mel list_php Date:August 30 2005 2:00pm
Subject:hierarchical db/depth?
View as plain text  
hi!
I'm still trying to organize an hierachical db (I saw the last article on 
mysql.com: 
http://dev.mysql.com/tech-resources/articles/hierarchical-data.hml).
I began working with what the author calls "adjency list model" (I think the 
nested set model is a bit too complex for what I want to do.In addition I 
found an equivalent schema in an other application which is close to 
mine....and working fine)
Basically, I have a table term (term_id, name), relation 
(relation_id,term_id1,term_id2,type_id) and a last table to identify the 
relations type id, relation_type (type_id,type_name).

I can retrieve all the info I need with that query:
SELECT t1.term_id2 AS lev0, term0.name AS parent0, trel1.type_name AS rel1, 
t1.term_id1 AS lev1, term1.name AS parent1, trel2.type_name AS rel2, 
t2.term_id1 AS lev2, term2.name AS parent2, trel3.type_name AS rel3, 
t3.term_id1 AS lev3, term3.name AS parent3
FROM relation AS t1
LEFT JOIN relation_type AS trel1
USING ( type_id )
LEFT JOIN term AS term0 ON ( t1.term_id2 = term0.term_id )
LEFT JOIN relation AS t2 ON t2.term_id2 = t1.term_id1
LEFT JOIN relation_type AS trel2
USING ( type_id )
LEFT JOIN term AS term1 ON ( t2.term_id2 = term1.term_id )
LEFT JOIN relation AS t3 ON t3.term_id2 = t2.term_id1
LEFT JOIN relation_type AS trel3
USING ( type_id )
LEFT JOIN term AS term2 ON ( t3.term_id2 = term2.term_id )
LEFT JOIN term AS term3 ON t3.term_id1 = term3.term_id
WHERE t1.term_id2 =1

It's just adding a new sub-part to the query for each level.
This is working fine on my data sample, because I know that I have exactly 4 
levels of depth.
I would like to know if there is a way to have a kind of "auto-extension" of 
the query if there is for example a fifth level?
Thanks for any help or tip,
melanie

_________________________________________________________________
Be the first to hear what's new at MSN - sign up to our free newsletters! 
http://www.msn.co.uk/newsletters

Thread
hierarchical db/depth?mel list_php30 Aug
  • Re: hierarchical db/depth?Peter Brawley30 Aug
  • RE: hierarchical db/depth?Edwin Cruz31 Aug