Mel,
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?
SQLdoesn't have recursion, so to avoid writing literal queries for each
number of levels you need either (i) something like an edge list, an
adjacency list, or a preorder tree traversal ('nested sets' as Celko
calls them) model, or (ii) write a query generator in an app language.
PB
-
mel list_php wrote:
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 mineand 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
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