select urls.id as urlId,
    count(case when s1.hit_type = 0 then 1 end) as aCount,
    count(case when s1.hit_type = 1 then 1 end) as bCount,
    count(case when s1.hit_type = 2 then 1 end) as cCount,
    count(distinct s1.source_id) as sourcesCount
from urls join stats s1 on urls.id = s1.url_id
where s1.hit_date >= '2017-12-12'
group by urls.id
order by aCount desc
limit 0,100;

mysql> show create table stats;

| stats | CREATE TABLE `stats` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `url_id` varchar(100) DEFAULT NULL,
  `hit_date` datetime DEFAULT NULL,
  `hit_type` tinyint(4) DEFAULT NULL,
  `source_id` bigint(20) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `url_id_idx` (`url_id`),
  KEY `source_id` (`source_id`),
  KEY `stats_hit_date_idx` (`hit_date`),
  CONSTRAINT `stats_ibfk_1` FOREIGN KEY (`url_id`) REFERENCES `urls` (`ID`),
  CONSTRAINT `stats_ibfk_2` FOREIGN KEY (`source_id`) REFERENCES `sources` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6027557 DEFAULT CHARSET=latin1 |

mysql> describe select...
| id | select_type | table   | type   | possible_keys                                                                                   | key     | key_len | ref                      | rows    | Extra                                        |
+----+-------------+---------+--------+-------------------------------------------------------------------------------------------------+---------+---------+--------------------------+---------+----------------------------------------------+
|  1 | SIMPLE      | s1      | ALL    | url_id_idx,stats_hit_date_idx                                                                   | NULL    | NULL    | NULL                     | 5869695 | Using where; Using temporary; Using filesort |
|  1 | SIMPLE      | urls    | eq_ref | PRIMARY,urls_email_idx,urls_status_idx,deptId_idx,deptId_status_email_idx                       | PRIMARY | 102     | db.s1.url_id             |     1   | Using index                                  |