=(, MySQL - rextester

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drop table if exists storage\\
create table storage (id int, product_id int, date_add datetime, date_remove datetime)\\
    
insert into storage
  (id, product_id, date_add, date_remove)
values
	(1, 10, timestamp '2018-04-02 08:28:43', timestamp '2018-04-03 07:21:08'),
	(2, 10, timestamp '2018-04-05 08:28:43', timestamp '2018-04-06 08:28:50'),
	(3, 10, timestamp '2018-04-01 08:28:43', timestamp '2018-04-05 08:28:50'),
	(4, 12, timestamp '2018-04-01 08:28:43', timestamp '2018-04-03 07:21:08'),
	(5, 12, timestamp '2018-04-04 08:28:43', timestamp '2018-04-04 10:28:43'),
    (6, 13, timestamp '2018-03-10 08:28:43', timestamp '2018-04-01 10:28:43'),
	(7, 13, timestamp '2018-03-01 08:28:43', timestamp '2018-04-01 10:28:43')\\

select
  product_id,
  sum(timestampdiff(second, greatest(date_add, date '2018-04-01'), least(date_remove, date '2018-04-06'))) / 60 / 60 / 24 as days
from storage
where date_add < date '2018-04-06' and date_remove >= date '2018-04-01'
group by product_id
order by product_id\\

drop table storage\\


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