Re: LEFT OUTER JOINS

We use functions to solve this problem. If you want to use "outer join"
by column ltg you can create function

CREATE FUNCTION outer_join_by_id_for_class_a(int) RETURNS class_a AS
'
SELECT * FROM class_a WHERE id = $1;
'
LANGUAGE 'sql';

Suppose you want to read field XXX from class_a, "outer joined" by
class_b.id_a = class_a.id
Then you can use it this way:

SELECT <some_fields>, xxx(outer_join_by_id_for_class_a(id_a)) FROM
class_b WHERE ....

It works fine for us, but probably there are more effitient solutions.

Regards
Pawel

Hoosain Madhi wrote:
>
> I would like to perform an outer join. I know that Postgres does not support
> Outer Joins and the work around is to use a combination of UNION ALL and SUB
> Queries.
>
> In particular I am struggling with the following scenario.
> There are three tables tbl_ltg, tbl_tgrp, tbl_c7links.
>
> tbl_tgrp references tbl_ltg with attributes (node,ltg)
> tbl_c7links references tbl_ltg with attributes (node,ltg)
>
> I have come up with the following SQL, but as you guessed, does not work.
> The fact that I request
> c.c7link in the first part of the query, it returns all c7links from
> tbl_c7links. Ideally I should set this to NULL and then request c.c7links in
> the second part of the query (line9). However the parser complains if I
> replace c.c7link with NULL in line 1.
>
> ----------------------------------------------------------------------------
> ------------
> 1 SELECT l.ltg, t.diu , t.tgno , t.cic , l.load_type , l.ltg_type, t.oml,
> c.c7link
> 2 FROM tbl_ltg l , tbl_tgrp t, tbl_c7links c
> 3 WHERE l.ltg=t.ltg
> 4 AND l.node=t.node
> 5 AND l.node='BCO'
> 6
> 7 UNION ALL
> 8
> 9 SELECT l.ltg, t.diu, NULL, NULL, NULL, NULL, NULL, c.c7link
> 10 FROM tbl_ltg l , tbl_tgrp t , tbl_c7links c
> 11 WHERE l.ltg NOT IN (SELECT ltg FROM tbl_c7links)
> 12 AND t.diu NOT IN (SELECT diu FROM tbl_c7links)
> 13 AND l.node='BCO'
>
> ORDER BY l.ltg
> ----------------------------------------------------------------------------
> ------------
>
> The tables are :
>
> tbl_ltg
> --------
> node ltg load_type ltg_type
> ---------+-------+-----------+----------+
> BCO | 1- 1 | 46 | LTGB |
> BCO | 1- 2 | 46 | LTGB |
> BCO | 1- 3 | 46 | LTGB |
>
> tbl_tgrp
> ---------
> node ltg diu tgno cic oml
> ---------+-------+-----------+----------+-------+-------+
> BCO | 1- 1 | 0 | MTNHAB | 7 | |
> BCO | 1- 1 | 1 | JSAMAB | 9 | |
> BCO | 1- 1 | 2 | | | |
> BCO | 1- 1 | 3 | | | |
> tbl_c7links
> -------------
> tbl_tgrp
>
> node c7link lcod silt ltg diu ts status
> ---------+----------+-----------+----------+-------+-------+-------+--------
> -+
> BCO | C7MTNMA | 0 | 12 | 1- 1 | 0 | 16 |
> |
> BCO | C7JSAMA | 1 | 100 | 1- 1 | 1 | 16 |
> |
>
> ----------------------------------------------------------------------------
> -----------------------
> --------------------------------------------OUTER JOIN RESULTS
> ------------------------------------
> ----------------------------------------------------------------------------
> -----------------------
>
> I need to a SQL statement that will return the following tuples:
> ltg diu tgno cic load_type ltg_type oml c7link
> silt lcod
> ------+-----+---------+-----+-----------+----------+---------+----------+---
> ---+-----+
> 1- 1 | 0 | MTNHAB | 7 | 46 | LTGB | | C7MTNMA | 12
> | 0 |
> 1- 1 | 1 | JSAMAB | 9 | 46 | LTGB | | C7JSAMA |
> 100 | 1 |
> 1- 1 | 2 | | | | | | |
> | |
> 1- 1 | 3 | | | | | | |
> | |
>
> Hoosain Madhi
> TELECOMMUNICATIONS ENGINEERING
> VODACOM PTY LTD
> tel : +27 11 653 5030
> fax : +27 11 653 5941
> email : hoosain(dot)madhi(at)vodacom(dot)co(dot)za