Re: Table transform query

pgsql-sql-owner(at)postgresql(dot)org wrote:

> Hi,
>
> I'm trying to find out how to transform this kind of table data
> (history of rental data in a firm):

...

I have answred my own question: yes, there is a pure SQL solution, with
a subselect:

CREATE TABLE foo (
serial integer,
delivery character(1),
date integer
);

INSERT INTO foo (serial, delivery, date) VALUES (1, 'L', 1);
INSERT INTO foo (serial, delivery, date) VALUES (2, 'L', 1);
INSERT INTO foo (serial, delivery, date) VALUES (3, 'L', 1);
INSERT INTO foo (serial, delivery, date) VALUES (1, 'R', 2);
INSERT INTO foo (serial, delivery, date) VALUES (2, 'R', 2);
INSERT INTO foo (serial, delivery, date) VALUES (4, 'L', 2);
INSERT INTO foo (serial, delivery, date) VALUES (5, 'L', 3);
INSERT INTO foo (serial, delivery, date) VALUES (3, 'R', 3);
INSERT INTO foo (serial, delivery, date) VALUES (4, 'R', 3);
INSERT INTO foo (serial, delivery, date) VALUES (1, 'L', 4);

-------------
select

f.serial,
f.date as dateL,
( select f2.date from foo as f2
where f2.serial = f.serial
and f2.date > f.date
and f2.delivery = 'R'
order by f2.date asc
limit 1
) as dateR

from foo as f
where f.delivery = 'L'
order by f.serial, f.date
-------------

I'm not sure if we could use a self-join here...

Cheers,

Philippe Lang