Date: Fri, 27 Jun 2003 09:08:54 -0500
From: Bruno Wolff III <bruno@wolff.to>
To: =?iso-8859-1?Q?Egy=FCd?= Csaba <csegyud@freemail.hu>
Cc: pgsql-sql@postgresql.org
Subject: Re: Getting all rows even if not a member of any groups
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On Fri, Jun 27, 2003 at 13:13:07 +0200,
  Együd Csaba <csegyud@freemail.hu> wrote:
> Hi,

Please don't reply to messages to start a new thread.

> I have a product table identified by its id field. There is a productgroups
> table with productisd, productgroupid fields. And I have a prod_in_pgr
> (productid, productgroupid) table which describes the membership of
> productgroups. Each product can be a member of zero or more productgroups,
> but one productgroup can contain a product only once.
> 
> I would like to list the following information:
>     productgroupid | productid | ... some other prouduct info | ...
> 
> I need all the products even if it is not a member in any productgroups. I
> need these information ordered by productgroup and then productid.
> --------------------------------
> An example:
> 
> select t_productgroups.name as pgroup,
>          t_products.id as productid
> from t_products
> join t_prod_in_pgr on (t_products.id=productid)
> join t_productgroups on (t_productgroups.id = t_prod_in_pgr.productgroupid)
> order by pgroup, productid;

I think you want something like:
select t_productgroups.name as pgroup,
         t_products.id as productid
from t_products
left join (t_prod_in_pgr
join t_productgroups on (t_productgroups.id = t_prod_in_pgr.productgroupid))
on (t_products.id=productid)
order by pgroup, productid;