group by query

       t_stamp       | total_charge | count
---------------------+--------------+-------
 2011-05-09 07:56:50 |        22650 |     1
 2011-05-09 09:28:15 |         6450 |     1
 2011-05-09 08:59:51 |        17850 |     1
 2011-05-11 10:15:00 |        13050 |     1
 2011-05-09 13:51:51 |         1950 |     1
 2011-05-09 22:27:31 |            0 |     1
 2011-05-09 23:47:58 |        29850 |     1
 2011-05-10 09:17:33 |          150 |     1
 2011-05-11 09:51:48 |         1350 |     1
 2011-05-09 22:39:10 |            0 |     1
 2011-05-09 15:31:07 |            0 |     1
 2011-05-11 09:32:58 |        29400 |     1
 2011-05-09 07:11:16 |        18750 |     1
 2011-05-09 23:51:16 |         1650 |     1
 2011-05-10 07:11:23 |        28650 |     1
 2011-05-10 08:00:50 |            0 |     1
 2011-05-10 17:02:39 |        25350 |     1
 2011-05-09 22:06:13 |         5700 |     1
 2011-05-09 22:47:59 |            0 |     1
 2011-05-09 09:12:34 |            0 |     1
 2011-05-10 09:00:13 |         4500 |     1
 2011-05-09 22:26:59 |            0 |     1
 2011-05-09 23:44:35 |         1800 |     1
 2011-05-10 21:35:36 |            0 |     1
 2011-05-09 15:12:13 |         2100 |     1
 2011-05-10 09:07:28 |        15900 |     1
 2011-05-09 15:28:22 |         8550 |     1
 2011-05-10 15:40:19 |        10950 |     1

question?
how can i create a query that groups by the date?
i want to have 'total_charge' according to date.

here is my query
select t_stamp, total_charge from mt.mt_batches where complete='t' and date(t_stamp) between 20110509 and 20110512;

thanks