Date: Fri, 2 Oct 2009 07:45:49 +0200
From: "A. Kretschmer" <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: right join problem
Message-ID: <20091002054548.GB22496@a-kretschmer.de>
References: <ddcb1c340910012233m41f6161kaac483c04ef4b320@mail.gmail.com>
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In response to Greenhorn :
> Hi,
> 
> I'm trying to retrieve all meter_id from table meter, and for meter_id
> without amount, I'd like it to show nothing, 'null'.  I've used right
> join here but it's not giving me my desired result.  Is there another
> way to do this?  Here's the query I'm trying.
> 
> Thanks in advance!
> 
> select m.meter_id, mp.meter_id, sum(amount_in_cents) as am
> from meter m
> right join transaction_mpark mp on (m.meter_id = mp.meter_id)
> where date_time between '2009-09-28 00:00:00' and '2009-10-04 23:59:59'
> group by m.meter_id, mp.meter_id
> order by m.meter_id

Use a left join instead?

test=*# select * from master;
 id |   name
----+----------
  1 | master 1
  2 | master 2
(2 rows)

test=*# select * from slave;
 id | value
----+-------
  1 |     1
  1 |     2
  1 |     3
(3 rows)

test=*# select m.id, s.id, sum(s.value) from master m right join slave s on (m.id=s.id) group by m.id, s.id;
 id | id | sum
----+----+-----
  1 |  1 |   6
(1 row)

test=*# select m.id, s.id, sum(s.value) from master m left join slave s on (m.id=s.id) group by m.id, s.id;
 id | id | sum
----+----+-----
  1 |  1 |   6
  2 |    |
(2 rows)


Andreas
-- 
Andreas Kretschmer
Kontakt:  Heynitz: 035242/47150,   D1: 0160/7141639 (mehr: -> Header)