Message-ID: <20020812151148.26186.qmail@web40013.mail.yahoo.com>
Date: Mon, 12 Aug 2002 08:11:48 -0700 (PDT)
From: Ludwig Lim <lud_nowhere_man@yahoo.com>
Subject: Re: Need Help for select
To: Andre Schubert <andre@km3.de>
Cc: PostgreSQL Mailing List <pgsql-sql@postgresql.org>
In-Reply-To: <20020812150640.4acd538b.andre@km3.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii


--- Andre Schubert <andre@km3.de> wrote:
> Hi all,
> 
> i need help to build a select query or
> plpgsql-fucntion
> for the following tables.
>> Is it possible to build a select query that selects
> d.name for each a.name where
> a.id = b.a_id and d.id = c.d_id and each b.c_id must
> exist in c.b_id.
> 
> Example:
> a:	      b:             c  :           d:
>  id | name      a_id | c_id    b_id | d_id    id | 
> name
> ----|-------  -------|-----  -------|----- 
> -----|--------
>  1  | A_Name1    1   |   1       1  |  1      1  |
> D_Name1
>  2  | A_Name2    1   |   2       2  |  1      2  |
> D_Name2
>  3  | A_Name3    2   |   1       3  |  2      3  |
> D_Name3
>  4  | A_Name4    3   |   3       4  |  2
>                  3   |   4       5  |  3
> 	         4   |   5
> 
> i wish to have to following result:
> --------|--------
> A_Name1 | D_Name1
> A_Name3 | D_Name2
> A_Name4 | D_Name3
> 
> I hope someone could understand the problem

You can use views to to simplify complicated queries

Create a view that will join table A & B

Create view view_ab(name,id) as
select name,c_id
from a,b
where id = c_id;

Create a view that will join table C & D

Create view view_cd(name2,id2) as
select name,b_id
from c,d
where id=d_id;

Create a query that will join the views "view_ab" and
"view_cd"

Select name,name2
from view_ab,view_cd
where id=id2;


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