insert 0 when combing tables?

[m b]

i'm really new at this and have the following question. say I have this table:

CREATE TABLE `transactions` (
  `date` date DEFAULT NULL,
  `category` enum('gas','food') DEFAULT NULL,
  `cost` float(10,2) DEFAULT NULL
) ENGINE=MyISAM;

with these inserts:

INSERT INTO `transactions` (`date`,`category`,`cost`) VALUES ('2010-09-01','food','20.00');
INSERT INTO `transactions` (`date`,`category`,`cost`) VALUES ('2010-09-10','gas','10.00');
INSERT INTO `transactions` (`date`,`category`,`cost`) VALUES ('2010-09-15','food','40.00');
INSERT INTO `transactions` (`date`,`category`,`cost`) VALUES ('2010-08-20','food','35.00');

producing a table that would look like this:

date 		category	cost
2010-09-01	food		20.00
2010-09-10	gas		10.00
2010-09-15	food		40.00
2010-08-20	food		35.00

i'm able to query to produce these two tables:

item	august
food	35.00

item	septemper
gas	10.00
food	60.00

but I would like to query to combine them and include zeros where relevant. i.e. i would like to produce a table like this:

item	august	septemper
gas	0.00	10.00
food	35.00	60.00

any suggestions? thanks!