CREATE TABLE `statistic` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `date_end` datetime NOT NULL,
  `date_start` datetime NOT NULL,
  PRIMARY KEY (`id`),
  KEY `statistic_date_end_new_6f3de8e3933125c_uniq` (`date_end`),
  KEY `statistic_date_start_new_35e1f6a6a8caae3_uniq` (`date_start`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

select max(col)+1 as crcol 
from 
   (
   select count(s.id) as col, s1.id as id1 from statistic as s 
   inner join statistic as s1 on s.id > s1.id 
   where (s.date_start between s1.date_start and s1.date_end or s.date_end between s1.date_start and s1.date_end) 
   group by s1.id
   ) 
as A

create view `change` as
select date_start `date`,  1 `value` from statistic
union all
select date_end         , -1         from statistic;

select c2.`date` `date`, sum(c1.`value`) conn_amount
from change c1, change c2
where c1.`date` <= c2.`date`
group by c2.`date`;