Message-ID: <429CD15B.2070503@ca.afilias.info>
Date: Tue, 31 May 2005 17:04:27 -0400
From: Andrew Hammond <ahammond@ca.afilias.info>
Organization: Afilias Canada Corp.
User-Agent: Debian Thunderbird 1.0.2 (X11/20050331)
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To: lucas@presserv.org
Cc: pgsql-sql@postgresql.org
Subject: Re: Sum() rows
References: <20050531133648.cypdc5lnjtc0wsws@www.presserv.org>
In-Reply-To: <20050531133648.cypdc5lnjtc0wsws@www.presserv.org>
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lucas@presserv.org wrote:
> Hi.
> How can I sum a row and show the sum for each row???
> For example, in a finances table that have the total movimentation(debit/credit)
> in the bank.
> 
> i.e:
> CREATE TABLE TB1 (id integer primary key, value numeric);
> insert into tb1 values (1,20);
> insert into tb1 values (2,2);
> insert into tb1 values (3,3);
> insert into tb1 values (4,17);
> insert into tb1 values (5,-0.5);
> insert into tb1 values (6,3);
> 
> I want a query that returns:
> -id- | --- value --- | --- subtot ---
>    1 |        20.00  |         20.00
>    2 |         2.00  |         22.00
>    3 |         3.00  |         25.00
>    4 |        17.00  |         42.00
>    5 |        -0.50  |         41.50
>    6 |         3.00  |         44.50
> 
> The subtot colum will be the "prev. subtot colum"+"value colum". :-/
> I dont know how to make the "subtot" colum, I tried to use the sum() function
> but it not works correctly.
> Any idea???

This kind of thing is often done using views and rules. For example,

CREATE TABLE tb1_real (
    id serial primary key,
    value numeric,
    subtot numeric
);

CREATE VIEW tb1 AS
SELECT id, value
FROM tb1_real;

CREATE RULE tb1_insert AS
ON INSERT TO tb1 DO INSTEAD
INSERT INTO tb1_real (id, value, subtot)
VALUES (COALESCE(NEW.id, nextval('tb1_real_id_seq')),
    NEW.value,
    NEW.value + COALESCE((SELECT subtot FROM tb1_real
                          ORDER BY id DESC LIMIT 1), 0));

/* ahammond@[local]:5432/ahammond =# */ INSERT INTO tb1 (value) VALUES (20);
INSERT 60812 1
/* ahammond@[local]:5432/ahammond =# */ INSERT INTO tb1 (value) VALUES
(-10);
INSERT 60813 1
/* ahammond@[local]:5432/ahammond =# */ SELECT * FROM tb1;
 id | value
- ----+-------
  1 |    20
  2 |   -10
(2 rows)

/* ahammond@[local]:5432/ahammond =# */ SELECT * FROM tb1_real;
 id | value | subtot
- ----+-------+--------
  1 |    20 |     20
  2 |   -10 |     10
(2 rows)

- --
Andrew Hammond    416-673-4138    ahammond@ca.afilias.info
Database Administrator, Afilias Canada Corp.
CB83 2838 4B67 D40F D086 3568 81FC E7E5 27AF 4A9A
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