Re: Breadth first traversal in PLSQL (How to implement Queue?)

Arg! One more change below

On Wed, 15 Dec 2004 21:48:57 -0500, Mike Rylander <mrylander(at)gmail(dot)com> wrote:
> On Wed, 15 Dec 2004 12:54:44 -0600, Richard Rowell
> <richard(at)bowmansystems(dot)com> wrote:
> > I have a table with a unary (recursive) relationship that represents a
> > hierarchy. With the gracious help of Mike Rylander I was able to port a
> > TSQL function that would traverse "up" the hierarchy to PL/SQL. Now I
> > need help porting the "down" the hierarchy function.
>
> Glad I could help!
>
> >
> > As implemented in TSQL I utilized a simple breadth first tree traversal.
> > I'm not sure how to replicate this in PL/SQL as I haven't figured out
> > how to implement the queue required for the breadth first algorithm. My
> > queue is declared "queue SETOF INTEGER" and I'm able to "SELECT INTO"
> > this variable. However when I try to delete the "current" value, I get
> > a syntax error. If I comment the delete out, I also get an error when I
> > try to fetch the "next" value from the front of the queue.
> >
>
> You probably want to use a temp table to hold the queue. Edits inline below.
>
> > Below is the function, followed by the psql output:
> >
> > CREATE OR REPLACE FUNCTION svp_getchildproviderids (INTEGER)
> > RETURNS SETOF INTEGER
> > AS '
> > DECLARE
> > parent_provider ALIAS FOR $1;
> > cid INTEGER;
>
> -- Comment out the next line...
> -- queue SETOF INTEGER;
>
> > BEGIN
>
> -- We need to use execute to create the queue, otherwise
> -- the OID will be cached and the next invocation will cause
> -- an exception.
> EXECUTE ''CREATE TEMP TABLE cid_queue
> (id SERIAL, cid INTEGER ) WITHOUT OIDS;'';
>
> > SELECT INTO cid count(*) FROM providers WHERE uid =parent_provider;
> > IF cid = 0 THEN
> > RAISE EXCEPTION ''Inexistent ID --> %'', parent_provider;
> > RETURN;
> > END IF;
> > cid := parent_provider;
> > LOOP
> > EXIT WHEN cid IS NULL;
> > RETURN NEXT cid;
>
> -- Put the CID into the queue
> EXECUTE ''INSERT INTO cid_queue VALUES
> ((SELECT uid FROM providers WHERE
> parent_id = '' ||
> quote_literal( cid ) || ''));'';
>
> -- We'll use EXECUTE to delete the current cid from the queue
> EXECUTE ''DELETE FROM cid_queue WHERE cid = '' ||
> quote_literal( cid ) || '';'';
>
> -- And a short loop to grab the next one
> FOR cid IN EXECUTE ''SELECT cid FROM cid_queue ORDER BY id LIMIT 1;''
> END LOOP;
>
> > END LOOP;

-- We need to drop the temp table, since this will probably be called
-- more than once in a transaction.
EXECUTE ''DROP TABLE cid_queue;'';

> > RETURN;
> > END;' LANGUAGE 'plpgsql';
>
> Let me know if that works. As before, it's untested, so YMMV... :)
>
> --
> Mike Rylander
> mrylander(at)gmail(dot)com
> GPLS -- PINES Development
> Database Developer
> http://open-ils.org
>

--
Mike Rylander
mrylander(at)gmail(dot)com
GPLS -- PINES Development
Database Developer
http://open-ils.org