> 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