Mysql : Finding empty time blocks between two dates and times? - mysql

Question

I wanted to find out user's availability from database table:
primary id | UserId | startdate | enddate
1 | 42 | 2014-05-18 09:00 | 2014-05-18 10:00
2 | 42 | 2014-05-18 11:00 | 2014-05-18 12:00
3 | 42 | 2014-05-18 14:00 | 2014-05-18 16:00
4 | 42 | 2014-05-18 18:00 | 2014-05-18 19:00
Let's consider above inserted data is user's busy time, I want to find out free time gap blocks from table between start time and end time.
BETWEEN 2014-05-18 11:00 AND 2014-05-18 19:00;
Let me add here schema of table for avoiding confusion:
Create Table availability (
pid int not null,
userId int not null,
StartDate datetime,
EndDate datetime
);
Insert Into availability values
(1, 42, '2013-10-18 09:00', '2013-10-18 10:00'),
(2, 42, '2013-10-18 11:00', '2013-10-18 12:00'),
(3, 42, '2013-10-18 14:00', '2013-11-18 16:00'),
(4, 42, '2013-10-18 18:00', '2013-11-18 19:00');
REQUIREMENT:
I wanted to find out free gap records like:
'2013-10-27 10:00' to '2013-10-28 11:00' - User is available for 1 hours and
'2013-10-27 12:00' to '2013-10-28 14:00' - User is available for 2 hours and
available start time is '2013-10-27 10:00' and '2013-10-27 12:00' respectively.

Answer 1

Here you go
SELECT t1.userId,
t1.enddate, MIN(t2.startdate),
MIN(TIMESTAMPDIFF(HOUR, t1.enddate, t2.startdate))
FROM user t1
JOIN user t2 ON t1.UserId=t2.UserId
AND t2.startdate > t1.enddate AND t2.pid > t1.pid
WHERE
t1.endDate >= '2013-10-18 09:00'
AND t2.startDate <= '2013-11-18 19:00'
GROUP BY t1.UserId, t1.endDate
http://sqlfiddle.com/#!2/50d693/1

Answer 2

Using your data, the easiest way is to list the hours when someone is free. The following gets a list of hours when someone is available:
select (StartTime + interval n.n hour) as FreeHour
from (select cast('2014-05-18 11:00' as datetime) as StartTime,
cast('2014-05-18 19:00' as datetime) as EndTime
) var join
(select 0 as n union all select 1 union all select 2 union all select 3 union all select 4 union all
select 5 union all select 6 union all select 7 union all select 8 union all select 9
) n
on StartTime + interval n.n hour <= EndTime
where not exists (select 1
from availability a
where StartTime + interval n.n hour < a.EndDate and
StartTime + interval n.n hour >= a.StartDate
);
EDIT:
The general solution to your problem requires denormalizing the data. The basic query is:
select thedate, sum(isstart) as isstart, #cum := #cum + sum(isstart) as cum
from ((select StartDate as thedate, 1 as isstart
from availability a
where userid = 42
) union all
(select EndDate as thedate, -1 as isstart
from availability a
where userid = 42
) union all
(select cast('2014-05-18 11:00' as datetime), 0 as isstart
) union all
(select cast('2014-05-18 19:00' as datetime), 0 as isstart
)
) t
group by thedate cross join
(select #cum := 0) var
order by thedate
You then just choose the values where cum = 0. The challenge is getting the next date from this list. In MySQL that is a real pain, because you cannot use a CTE or view or window function, so you have to repeat the query. This is why I think the first approach is probably better for your situation.

Answer 3

The core query can be this. You can dress it up as you like, but I'd handle all that stuff in the presentation layer...
SELECT a.enddate 'Available From'
, MIN(b.startdate) 'To'
FROM user a
JOIN user b
ON b.userid = a.user
AND b.startdate > a.enddate
GROUP
BY a.enddate
HAVING a.enddate < MIN(b.startdate)
For times outside the 'booked' range, you have to extend this a little with a UNION, or again handle the logic at the application level