Detect overlapping date ranges from the same table

I have a table with the following data

PKey  Start       End         Type
====  =====       ===         ====
01    01/01/2010  14/01/2010  S
02    15/01/2010  31/01/2010  S
03    05/01/2010  06/01/2010  A

And want to get the following results

PKey  Start       End         Type
====  =====       ===         ====
01    01/01/2010  14/01/2010  S
03    05/01/2010  06/01/2010  A

Any ideas on where to start? A lot of the reading I've done suggests I need to create entries and for each day and join on matching days, is this the only way?

Solution 1:

If you already have entries for each day that should work, but if you don't the overhead is significant, and if that query is used often, if will affect performance.

If the data is in this format, you can detect overlaps using simple date arithmetic, because an overlap is simply one interval starting after a given interval, but before the given is finished, something like

select dr1.* from date_ranges dr1
inner join date_ranges dr2
on dr2.start > dr1.start -- start after dr1 is started
  and dr2.start < dr1.end -- start before dr1 is finished

If you need special handling for interval that are wholly within another interval, or you need to merge intervals, i.e.

PKey  Start       End         Type
====  =====       ===         ====
01    01/01/2010  20/01/2010  S
02    15/01/2010  31/01/2010  S

yielding

Start       End         Type
=====       ===         ====
01/01/2010  31/01/2010  S

you will need more complex calculation.

In my experience with this kind of problems, once you get how to do the calculation by hand, it's easy to transfer it into SQL :)

Solution 2:

When I needed to compare two time spans in SQL for overlap, here are the four scenarios I could think of:

1. Span1 start is between Span2 start and Span2 end
2. Span1 end is between Span2 start and Span2 end
3. Span1 start and end are both between Span2 start and Span2 end
4. Span2 start and end are both between Span1 start and Span1 end

Here is the OR statement I created to capture these scenarios (in my case Oracle SQL):

and (
    s1.start between s2.start and s2.end
    OR
    s1.end between s2.start and s2.end
    OR
    s2.start between s1.start and s1.end
)

Solution 3:

Perhaps:

SELECT A.PKey, A.Start, A.End, A.Type
FROM calendar AS A, calendar AS B
WHERE (p.pkey<>a.pkey
AND b.start>=a.start
AND b.end<=a.end)
OR (b.pkey<>a.pkey
AND b.start<=a.start
AND b.end>=a.end)