Re: query to select a linked list

On 5/9/07, Louis-David Mitterrand <vindex+lists-pgsql-sql(at)apartia(dot)org>
wrote:
>
> Hi,
>
> To build a threaded forum application I came up the following schema:
>
> forum
> ------
> id_forum | integer| not null default
> nextval('forum_id_forum_seq'::regclass)
> id_parent| integer|
> subject | text | not null
> message | text |
>
> Each message a unique id_forum and an id_parent pointing to the replied
> post (empty if first post).
>
> How can I build an elegant query to select all messages in a thread?
>
> Thanks,
>

Unlike Oracle, PostgreSQL doesn't have anything like a connect by so you
would need to write your own stored procedure for that (if new versions of
PostgreSQL will have connect by, let me know guys).

What I did was add a little redundancy to my forum tables and had a table
structure kind of like this:

forum
forum_id BIGSERIAL PK,
name VARCHAR(50)

forum_topic
forum_topic_id BIGSERIAL PK,
forum_id BIGINT FK to forum

forum_post
forum_post_id BIGSERIAL PK,
create_dt TIMESTAMP,
subject VARCHAR(255),
message TEXT,
forum_topic_id BIGINT FK to forum_topic

and if you want threading, you add a parent_forum_post_id to forum_post
(this is where you get the redundancy since only the top forum_post record
needs a reference to forum_topic and forum_topic wouldn't even really be
needed.

-Aaron

--
==================================================================
Aaron Bono
Aranya Software Technologies, Inc.
http://www.aranya.com
http://codeelixir.com
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