Subject: Breadth first traversal in PLSQL (How to implement Queue?)
From: Richard Rowell <richard@bowmansystems.com>
To: PostgreSQL SQL <pgsql-sql@postgresql.org>
Content-Type: text/plain
Date: Wed, 15 Dec 2004 12:54:44 -0600
Message-Id: <1103136884.9908.22.camel@richard>
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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.  

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.

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;
 queue SETOF INTEGER;
BEGIN
   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;
       SELECT INTO queue uid FROM providers WHERE parent_id = cid;
       DELETE FROM queue WHERE queue.queue = cid;
       SELECT INTO cid * FROM queue LIMIT 1;
   END LOOP;
   RETURN;
END;' LANGUAGE 'plpgsql';

sp_demo_505=# select * from svp_getchildproviderids(1);
ERROR:  syntax error at or near "$1" at character 14
CONTEXT:  PL/pgSQL function "svp_getchildproviderids" line 16 at SQL
statement


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