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Paragon Corporation
Using PostgreSQL User-Defined Functions to solve the Tree Problem

The Problem: Suppose you are tracking supplies and have a field called si_item and another called si_parentid. The parent keeps track of what subclass a supply item belongs to. E.g. you have paper parent that has subclasses such as recycled, non-recycled. When someone takes supplies, you want to return the fully qualified name e.g. Paper->Recycled->20 Lb

Below is what the structure of your table looks like.

si_id int, si_parentid int, si_item. In your table are the following entries
si_id si_parentid si_item
1   Paper
2 1 Recycled
3 2 20 lb
4 2 40 lb
5 1 Non-Recycled
6 5 20 lb
7 5 40 lb
8 5 Scraps


Now everyone at work is asked to throw all their paper in the recycle bin for recycling. With recycling, we are told we will save trees and have plentiful amounts of paper. John loves his paper and doesn't want it to be recycled. He surely doesn't want his beautiful paper to get into someone else's hands. So what he does is wrap his paper in styrofoam and throw it in the recycle bin. He thinks (Hee hee - that'll teach them to ask me to give up my paper). Little does John know that there is are other Johns and Janes in the halls thinking the same thing.

The function that will display the fully qualified name is below . The function looks as follows
CREATE FUNCTION cp_getitemfullname(int8) RETURNS varchar AS 'DECLARE
itemid ALIAS FOR $1;
itemfullname varchar(255);
itemrecord RECORD;
BEGIN
    SELECT s.* INTO itemrecord FROM supplyitem s  where si_id=itemid;
     itemfullname := itemfullname + itemrecord.si_item;
     IF itemrecord.si_parentid IS NOT NULL  THEN
           itemfullname := cp_getitemfullname(itemrecord.si_parentid) + ''->'' + itemfullname ;
           RETURN itemfullname;
     ELSE
           RETURN itemfullname;
     END IF;
END'  LANGUAGE 'plpgsql'



To figure out what paper John will ask for SELECT cp_getitemfullname(8) As thename This returns Paper->Non-Recycled->Scraps

Quelle: Paragon Corporation

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