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* Utility of recursive queries?
@ 2004-04-09 14:33 James Robinson <jlrobins@socialserve.com>
0 siblings, 2 replies; 3+ messages in thread
From: James Robinson @ 2004-04-09 14:33 UTC (permalink / raw)
To: pgsql-sql
Would recursive queries be the trick to doing things like unwinding a
linked-list to either the head or tail, with:
create table list (
id int primary key,
parent int references list(id)
);
insert into list values (1, null); -- head of chain in list
insert into list values (2, 1); -- 1st child
insert into list values (3, 2); -- second child
Given a reference to id=3, would a recursive query be the trick to
unrolling the list to discover id=1 as the head using a SQL one-liner?
Is discovery possible in straight SQL w/o resorting to stored
procedures (or modifying the table schema to directly point)? And,
finally, would any potential recursive query implementation be
noticably more efficient that a straightforward implementation in
plpgsql, such as:
create or replace function find_head(int) returns int as '
DECLARE
cur_par INT;
prev_par INT;
BEGIN
prev_par := $1;
cur_par := parent from list where id = $1;
WHILE cur_par is not null LOOP
prev_par := cur_par;
cur_par := parent from list where id = prev_par;
END LOOP;
return prev_par;
END;
' language 'plpgsql';
----
James Robinson
Socialserve.com
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Utility of recursive queries?
@ 2004-04-09 16:07 Josh Berkus <josh@agliodbs.com>
parent: James Robinson <jlrobins@socialserve.com>
1 sibling, 0 replies; 3+ messages in thread
From: Josh Berkus @ 2004-04-09 16:07 UTC (permalink / raw)
To: James Robinson <jlrobins@socialserve.com>; pgsql-sql
James,
> Would recursive queries be the trick to doing things like unwinding a
> linked-list to either the head or tail, with:
Yes. Also check out contrib/ltree and contrib/tablefunc in your handy-dandy
PostgreSQL source code.
--
Josh Berkus
Aglio Database Solutions
San Francisco
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Utility of recursive queries?
@ 2004-04-09 16:35 Tom Lane <tgl@sss.pgh.pa.us>
parent: James Robinson <jlrobins@socialserve.com>
1 sibling, 0 replies; 3+ messages in thread
From: Tom Lane @ 2004-04-09 16:35 UTC (permalink / raw)
To: James Robinson <jlrobins@socialserve.com>; +Cc: pgsql-sql
James Robinson <jlrobins@socialserve.com> writes:
> Given a reference to id=3, would a recursive query be the trick to
> unrolling the list to discover id=1 as the head using a SQL one-liner?
I think you could do it, but don't have the syntax in my head.
> would any potential recursive query implementation be
> noticably more efficient that a straightforward implementation in
> plpgsql
Most likely not ...
regards, tom lane
^ permalink raw reply [nested|flat] 3+ messages in thread
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2004-04-09 14:33 Utility of recursive queries? James Robinson <jlrobins@socialserve.com>
2004-04-09 16:07 ` Josh Berkus <josh@agliodbs.com>
2004-04-09 16:35 ` Tom Lane <tgl@sss.pgh.pa.us>
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