Re: Breadth first traversal in PLSQL (How to implement Queue?) - Mailing list pgsql-sql

Arg! One more change below

On Wed, 15 Dec 2004 21:48:57 -0500, Mike Rylander <mrylander@gmail.com> wrote:
> On Wed, 15 Dec 2004 12:54:44 -0600, Richard Rowell
> <richard@bowmansystems.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@gmail.com
> GPLS -- PINES Development
> Database Developer
> http://open-ils.org
> 


-- 
Mike Rylander
mrylander@gmail.com
GPLS -- PINES Development
Database Developer
http://open-ils.org