Identifying Overlapping time periods in SQL Server

Question

I have the following sample data

begin_date              end_date
-------------------------------------------
2014-08-27 07:10:00     2014-08-27 07:30:00
2014-08-27 07:30:00     2014-08-27 07:50:00
2014-08-27 07:40:00     2014-08-27 08:00:00
2014-08-27 07:50:00     2014-08-27 08:10:00
2014-08-27 08:10:00     2014-08-27 08:30:00
2014-08-27 08:30:00     2014-08-27 08:50:00
2014-08-27 08:30:00     2014-08-27 08:50:00

I want to identify overlapping time periods.

The expected output is

2014-08-27 07:30:00     2014-08-27 07:50:00
2014-08-27 07:40:00     2014-08-27 08:00:00
2014-08-27 07:50:00     2014-08-27 08:10:00
2014-08-27 08:30:00     2014-08-27 08:50:00
2014-08-27 08:30:00     2014-08-27 08:50:00

(2014-08-27 08:30:00 2014-08-27 08:50:00 overlap with another pair of same data itself)

Please help me out..

Answer 1

Two time periods A and B overlap iff (begin(A) < end(B)) && (end(A) >= begin(B)) . Does that help?

Maybe try something like this:

select p1.begin_date, p1.end_date, ' overlaps ', p2.begin_date, p2.end_date
from periodTable p1
inner join periodTable p2
    on p1.begin_date < p2.end_date
    and p1.end_date >= p2.begin_date

Edit:

In response to Tanner's comment, I suggest an elaborated version of the above:

select p1.begin_date, p1.end_date
from periodTable p1
inner join periodTable p2
    on p1.begin_date < p2.end_date
    and p1.end_date > p2.begin_date
group by p1.begin_date, p1.end_date
having count(*) > 1

This will yield all overlapping periods , but not the individual records from the table, that is, each period will only be returned once. (This corresponds to the puristic relational algebra view and is a result of the lack of a primary key.)

Answer 2

Try this :

SELECT  REsult.DtFrom, REsult.DtTo
FROM
(
SELECT DtFrom, DtTo, CASE WHEN DtFrom <= cast((LAG(DtTo) OVER(ORDER BY DtFrom, DtTo)) as datetime)
THEN 1 ELSE 0 END AS IsOverlapping
 FROM 
dbo.Dates_Overlap
) AS REsult
WHERE IsOverlapping = 1 
ORDER BY DtFrom, DtTo;