Join table with itself for heirarchial system? - Mailing list pgsql-sql

From Benjamin Smith
Subject Join table with itself for heirarchial system?
Date
Msg-id 200307161834.08104.bens@effortlessis.com
Whole thread Raw
Responses Re: Join table with itself for heirarchial system?  (Oleg Bartunov <oleg@sai.msu.su>)
List pgsql-sql
Can you query a set of nested entries to simulate a heirarchial system with a 
single query? 

I'm building a nested category table with a definition like below" 

CREATE TABLE category ( 
id serial, 
parent integer not null, 
title varchar); 

Idea is that we can "nest" categories so that we have 

id         parent        title
----------------------------------------------
1        0            Clothing
2        1            Shirts
3        1            Pants
4        1            Socks
5        4            Male
6        4            Silk 

So that, for example, id 6 would be 

Clothing -> Socks -> Silk. 

So far, I've only been able to derive this with 3 queries - 1 to get the 
parent for id #6 (Silk) another to get the parent for id #4 (Socks) and 
finally for id #1 (Clothing) and since parent ==0 I stop. 

This seems wasteful - can this be done in a single query? 


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