CREATE TABLE `stat` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `src_id` smallint(6) unsigned NOT NULL,
  `date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `result` smallint(2) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  KEY `src_id` (`src_id`)
) ENGINE=InnoDB AUTO_INCREMENT=732670 DEFAULT CHARSET=utf8

188 rows in set (1 hour 5 min 25.14 sec)

explain select * from `stat` s1 left join `stat` s2 on s2.id > s1.id and s2.src_id = s1.src_id  where s2.id is null;
+----+-------------+-------+------+--------------------------+--------+---------+----------------------+--------+-------------------------+
| id | select_type | table | type | possible_keys            | key    | key_len | ref                  | rows   | Extra                   |
+----+-------------+-------+------+--------------------------+--------+---------+----------------------+--------+-------------------------+
|  1 | SIMPLE      | s1    | ALL  | NULL                     | NULL   | NULL    | NULL                 | 963498 | NULL                    |
|  1 | SIMPLE      | s2    | ref  | PRIMARY,src_id,id_src_id | src_id | 2       | simple_mon.s1.src_id |   2474 | Using where; Not exists |
+----+-------------+-------+------+--------------------------+--------+---------+----------------------+--------+-------------------------+
2 rows in set (0.00 sec)

SELECT src_id, MAX(date), result FROM `stat` GROUP BY src_id