Date: Fri, 1 Dec 2006 15:44:58 +0100
From: "A. Kretschmer" <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: Setting boolean column based on cumulative integer value
Message-ID: <20061201144458.GA13639@a-kretschmer.de>
References: <9d8bdcf30612010550o3a5721lefc366e4984fd145@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <9d8bdcf30612010550o3a5721lefc366e4984fd145@mail.gmail.com>
User-Agent: Mutt/1.5.9i

am  Sat, dem 02.12.2006, um  0:50:37 +1100 mailte Markus Juenemann folgendes:
> I've got a bit of a tricky (for me!) problem. The example below is
> completely ficticious but
> describes my real problem in a way which might be easier to understand.
> 
> Imagine the table contains a list of passenger wanting to get on a
> small(!) plane.
> The plane can carry at most 200kg of passengers and will be filled
> strictly on a first-come
> first-serve basis - well, check-in staff is a bit stupid ;-). So what
> needs to be done is to set the 'gets_seat' column to true until the
> weight limit is reached.

With your example, i wrote a little function for this:

---%<------
create or replace function check_wight( out id int,
                                        out name text,
                                        out weight int,
                                        out gets_seat boolean ) returns setof record as $$
declare rec record;
        sum int;
begin
        sum = 0;
        for rec in select * from passenger_queue order by id LOOP
                id = rec.id;
                name = rec.name;
                weight = rec.weight;
                sum = sum + weight;
                if sum < 200 then
                        gets_seat='t'::bool;
                else
                        gets_seat='f'::bool;
                end if;
                return next ;
        end loop;
end
$$ language plpgsql;
---%<------


test=# select * from passenger_queue;
 id | name  | weight | gets_seat
----+-------+--------+-----------
  1 | Peter |     75 | f
  2 | Mary  |     50 | f
  3 | John  |     70 | f
  4 | Steve |     80 | f
(4 rows)

test=# select * from check_wight();
 id | name  | weight | gets_seat
----+-------+--------+-----------
  1 | Peter |     75 | t
  2 | Mary  |     50 | t
  3 | John  |     70 | t
  4 | Steve |     80 | f
(4 rows)


HTH, Andreas
-- 
Andreas Kretschmer
Kontakt:  Heynitz: 035242/47215,   D1: 0160/7141639 (mehr: -> Header)
GnuPG-ID:   0x3FFF606C, privat 0x7F4584DA   http://wwwkeys.de.pgp.net