PostgreSQL: using row_number() in paged output - php

Question

I have a PHP script displaying a list of players sorted by their "virtual money":
$sth = $db->prepare("
select u.id,
u.first_name,
u.city,
u.avatar,
m.money,
u.login > u.logout as online
from pref_users u, pref_money m where
m.yw=to_char(current_timestamp, 'IYYY-IW') and
u.id=m.id
order by m.money desc
limit 20 offset ?
");
$sth->execute(array($_GET['offset']));
To show a player position in the list I use a PHP variable $pos which is incremented in a loop while printing their names and further data.
I would like to have that position in the SQL statement instead of PHP for various reasons. So I'm trying the following:
$sth = $db->prepare("
select u.id,
row_number() + ? as pos,
u.first_name,
u.city,
u.avatar,
m.money,
u.login > u.logout as online
from pref_users u, pref_money m where
m.yw=to_char(current_timestamp, 'IYYY-IW') and
u.id=m.id
order by m.money desc
limit 20 offset ?
");
$sth->execute(array($_GET['offset'], $_GET['offset']));
But get the ERROR: window function call requires an OVER clause
I'm trying to add over(m.money) but get a syntax error.
I'm probably misunderstanding the Window Functions doc.

Answer 1

Check the user notes on: http://www.postgresql.org/docs/8.4/interactive/functions-window.html
You will need the Over() to contain the same order by clause as the whole query:
$sth = $db->prepare("
select u.id,
row_number() OVER (order by m.money desc) + ? as pos,
u.first_name,
u.city,
u.avatar,
m.money,
u.login > u.logout as online
from pref_users u, pref_money m where
m.yw=to_char(current_timestamp, 'IYYY-IW') and
u.id=m.id
order by m.money desc
limit 20 offset ?
");
$sth->execute(array($_GET['offset'], $_GET['offset']));

Answer 2

You want row_number() OVER (ORDER BY m.money) + ? etc.