Zkuste vytvořit vlastní agregační funkci jako:
CREATE FUNCTION quota_calc_func(numeric, numeric, numeric) -- carry over, daily usage and daily quota
RETURNS numeric AS
$$
SELECT GREATEST(0, $1 + $3 - $2);
$$
LANGUAGE SQL STRICT IMMUTABLE;
CREATE AGGREGATE quota_calc( numeric, numeric ) -- daily usage and daily quota
(
SFUNC = quota_calc_func,
STYPE = numeric,
INITCOND = '0'
);
WITH t(x, y) AS (
VALUES (2, '2013-09-16'),
(0, '2013-09-17'),
(3, '2013-09-18'),
(0, '2013-09-19'),
(7, '2013-09-20'),
(1, '2013-09-21'),
(0, '2013-09-22'),
(2, '2013-09-23'),
(1, '2013-09-24'),
(9, '2013-09-25')
)
SELECT x, y, quota_calc(x, 2) over (order by y)
FROM t;
Může obsahovat chyby, netestovali jsme to.