Comparing date ranges

Question

In mysql, If I have a list of date ranges (range-start and range-end). e.g.

10/06/1983 to 14/06/1983

15/07/1983 to 16/07/1983

18/07/1983 to 18/07/1983

And I want to check if another date range contains ANY of the ranges already in the list, how would I do that?

e.g.

06/06/1983 to 18/06/1983 = IN LIST

10/06/1983 to 11/06/1983 = IN LIST

14/07/1983 to 14/07/1983 = NOT IN LIST

Answer 1

This is a classical problem, and it's actually easier if you reverse the logic.

Let me give you an example.

I'll post one period of time here, and all the different variations of other periods that overlap in some way.

           |-------------------|          compare to this one
               |---------|                contained within
           |----------|                   contained within, equal start
                   |-----------|          contained within, equal end
           |-------------------|          contained within, equal start+end
     |------------|                       not fully contained, overlaps start
                   |---------------|      not fully contained, overlaps end
     |-------------------------|          overlaps start, bigger
           |-----------------------|      overlaps end, bigger
     |------------------------------|     overlaps entire period

on the other hand, let me post all those that doesn't overlap:

           |-------------------|          compare to this one
     |---|                                ends before
                                 |---|    starts after

So if you simple reduce the comparison to:

starts after end
ends before start

then you'll find all those that doesn't overlap, and then you'll find all the non-matching periods.

For your final NOT IN LIST example, you can see that it matches those two rules.

You will need to decide wether the following periods are IN or OUTSIDE your ranges:

           |-------------|
   |-------|                       equal end with start of comparison period
                         |-----|   equal start with end of comparison period

If your table has columns called range_end and range_start, here's some simple SQL to retrieve all the matching rows:

SELECT *
FROM periods
WHERE NOT (range_start > @check_period_end
           OR range_end < @check_period_start)

Note the NOT in there. Since the two simple rules finds all the non-matching rows, a simple NOT will reverse it to say: if it's not one of the non-matching rows, it has to be one of the matching ones.

Applying simple reversal logic here to get rid of the NOT and you'll end up with:

SELECT *
FROM periods
WHERE range_start <= @check_period_end
      AND range_end >= @check_period_start

Answer 2

Taking your example range of 06/06/1983 to 18/06/1983 and assuming you have columns called start and end for your ranges, you could use a clause like this

where ('1983-06-06' <= end) and ('1983-06-18' >= start)

i.e. check the start of your test range is before the end of the database range, and that the end of your test range is after or on the start of the database range.

Answer 3

If your RDBMS supports the OVERLAP() function then this becomes trivial -- no need for homegrown solutions. (In Oracle it apparantly works but is undocumented).

Answer 4

In your expected results you say

06/06/1983 to 18/06/1983 = IN LIST

However, this period does not contain nor is contained by any of the periods in your table (not list!) of periods. It does, however, overlap the period 10/06/1983 to 14/06/1983.

You may find the Snodgrass book (http://www.cs.arizona.edu/people/rts/tdbbook.pdf) useful: it pre-dates mysql but the concept of time hasn't changed ;-)

Answer 5

lassevk: you should enclose this logic as a method call in Java/.Net/xxxx, name it the DateRange Pattern (everyone loves patterns!), write a book on it and then make an easy million bucks. And then give me 10% of it.