тебе нужен GROUP BY
например
CREATE TABLE IF NOT EXISTS `ForgeRock` (
`id` int(11) DEFAULT NULL,
`site` varchar(128) DEFAULT NULL,
`date` date DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `ForgeRock` (`id`, `site`, `date`) VALUES
(1, 'site1.ru', '2016-02-13'),
(2, 'site1.ru', '2016-03-13'),
(3, 'site2.ru', '2016-02-13'),
(4, 'site2.ru', '2016-02-13'),
(5, 'site1.ru', '2016-02-13'),
(6, 'site2.ru', '2016-03-13'),
(7, 'site1.ru', '2016-02-13');
тогда запрос
SELECT `date`, `site`, COUNT(`id`)
FROM ForgeRock
WHERE `site`= "site1.ru"
GROUP BY `date`
ORDER BY `date` DESC