From: Ben K. <bkim@coe.tamu.edu>
To: Ray Madigan <ray@madigans.org>
Cc: Pgsql-Sql-Owner <pgsql-sql-owner@postgresql.org>
Cc: Marc G. Fournier <scrappy@hub.org>
Cc: pgsql-sql@postgresql.org
Subject: Re: Linked List
Date: Sun, 30 Apr 2006 20:29:26 -0500 (CDT)
Message-ID: <Pine.GSO.4.64.0604302014590.22531@coe.tamu.edu> (raw)
In-Reply-To: <IEELLOAPJFACBDBGELGHKEJPEDAA.ray@madigans.org>
References: <IEELLOAPJFACBDBGELGHKEJPEDAA.ray@madigans.org>
> I have a table that I created that implements a linked list. I am not an
> expert SQL developer and was wondering if there are known ways to traverse
> the linked lists. The table contains many linked lists based upon the head
> of the list and I need to extract all of the nodes that make up a list. The
> lists are simple with a item and a link to the history item so it goes kind
> of like:
>
> 1, 0
> 3, 1
> 7, 3
> 9, 7
> ...
I missed "The table contains many linked lists", so wanted to do another
try. I guess there should be a better way, but what if you do this?
1)
Assuming your table has two columns (n int, p int), do
create table tmplist (n int, p int);
2)
drop function traverse(integer);
create or replace function traverse (integer)
returns integer as
$$
declare
x int;
begin
x := $1;
while x is not null loop
select n into x from linkedlist where p = x;
insert into tmplist (select * from links where p=x);
-- or do any processing
end loop;
return 1 ;
end;
$$
language plpgsql;
3)
select traverse(0);
select * from tmplist;
0 - 1 - 4 - 8 - 12 ...
delete from tmplist;
select traverse(2);
select * from tmplist;
2 - 3 - 5 - 6 - ...
(where 0 or 2 is the heads of the linked lists in the table, which you
want to traverse)
I'd appreciate any insight if there's a better way but somehow it was not
possible to return setof int from within while loop whereas it was
possible from within a for loop. I didn't find a way to deliver the
templist table name as argument. (Somehow there seemed to be a bug(?)
there)
Regards,
Ben K.
Developer
http://benix.tamu.edu
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To: pgsql-sql@postgresql.org
Cc: bkim@coe.tamu.edu, ray@madigans.org, pgsql-sql-owner@postgresql.org, scrappy@hub.org
Subject: Re: Linked List
In-Reply-To: <Pine.GSO.4.64.0604302014590.22531@coe.tamu.edu>
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