hubert depesz lubaczewski wrote:
there have been a discussions about how posdtgresql needs 'with
recursive' queries.
not that i would like to object the idea (new feature is always a
good thing), but is anybody able to show me real usage of this kind of
queries?
as i see it the only usage for 'with recursive' is when one have a
tree-structure stored as:
create table objects (id serial primary key, parent_id int references
objects (id), ...)
and one want to do some "deep queries" without client-side
recursion/loops.
is it the only thing 'with recursive' is useful for? i mean it sounds
unrealistic given that better data-structures for tree hierarchies
have been proposed and implemented.
Better? I think perhaps different. There is materialized path, which
requires a very problematic unlimited-length column to hold the path,
and there is upper/lower bounds, which again requires client-side
row-by-row processing. Both have the unpleasant problem that changes to
one row may affect many others.
AFAIK, the "WITH RECURSE" allows the simplest data structure, being
key/parent_key. The best benefit of this method is that it is a simple
foreign key and no action on a row ever affects another row, unlike the
other two. If we could query out a list using WITH RECURSE it would
become very powerful.
best regards,
depesz
--
Kenneth Downs
Secure Data Software, Inc.
www.secdat.com / www.andromeda-project.org
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